Publications
Abstract for Society of Mining, Metallurgy and Exploration (SME) February 2007 meeting in Denver, CO.
Green Biosurfactants for Benign Mineral processing
P. Somasundaran 1 , Lei Zhang 3, Puspendu Deo 4, Jing Wang 1. and Richard A Gross 2, (1) Industry/University Cooperative Research Center for Surfactants, Columbia University, 500 W 120th Street, 910 S.W. Mudd, New York, NY 10027, Fax: 212-854-8362, ps24@columbia.edu, (2) NSF-I/UCRC Center for Biocatalysis and Bioprocessing of Macromolecules,Polytechnic University, (3) Akzo Nobel Chemicals, (4) CP Kelco
Biosurfactants formed by fermentation of renewable resources are “environmentally friendly” compounds that can modify mineral wettability suitably for use as collectors and modifiers. Colloidal and interfacial properties, such as aggregation, surface tension reduction and adsorption of natural sophorolipid surfactants, were investigated in this work to determine the role of alkyl moieties in formation of nanodomains on surfaces. Interestingly, these surfactants were found to adsorb selectively on certain substrates such as alumina but only weakly on others such as silica. We have also explored unique interfacial and colloidal properties of polysaccharides that are hydrophobically modified. Hydroxyethyl cellulose and its hydrophobically modified derivatives were studied systematically at talc-water interfaces using a combination of spectroscopic, microscopic, electrostatic adsorption and molecular modeling. The mechanism of talc-polysaccharide interactions was also explored. Modified interfacial and colloidal environments are indeed important in controlling adsorption and thereby flotation as well as dispersion/flocculation. Thus, solloidal (surface aggregate) structures formed by these compounds on solid substrates make them attractive candidates for use in mineral beneficiation as well as for pollution abatement techniques such as soil remediation and bioremediation.
Abstract for National Conference on Polymers, December 17-20, 2006 Pune, India
Effect of Modifying Functional Groups on Interfacial Behaviour of Hybrid Silicone Polymers
Somil Mehta,1 P. Somasundran,1
Columbia University, New York
Omprakash Yemul,2 Ravi Kulkarni2*
Elkay Chemicals Pvt Ltd, Pune, India.
Abstract
Polysiloxanes, are useful polymers, because of their high chemo-,
thermo- stability and nontoxicity. The desired properties can be
achieved by attaching suitable organic group to silicones. Such
Organic/Inorganic hybrid silicone polymers are increasingly used
in cosmetics; inks, paints, and fabric care applications due to
their special Si - O bond characteristics. Though widely used, their
utilization has mainly been empirical due to lack of fundamental
knowledge. In most of the earlier studies the hydrophilic modification
of silicones are based on non - ionic moieties. There is little
information available about their ionic counterparts. The present
work is focused on the effects of functionality on the conformation
of chains at the air-water interface. The structures of functionally
modified silicones have been presented in (Figure 1).
Figure 1 Structures of functionally modified silicones
Amino modified polymeric silicone (AMS) was synthesized from decamethyl
cyclopentasiloxane (D5), tetramethyl ammonium hydroxide, and amino
siloxane using equilibration process. The reactants were selected
such that to have only one amino group per side chain. The ratio
of reactants was adjusted such as to give m:n ratio of approximately
7.5:1 (figure 1) and the viscosity of the polymer was 65 cps. Quaternized
amino silicone (QAS) was synthesized by methylation of the amine
using methyl tosylate while acid modified silicone (IMS) has been
carried out by reacting with itaconic acid (figure 1).
Hydrophilically grafted silicone polymers form monolayers at air-water interface, which is stabilized by interaction of functional groups that are submerged in water subphase. It was observed that the shape of the chain depends on the available area at the interface and there are conformational changes with increase in molecules per unit area. Unlike poly(dimethylsiloxane) (PDMS), which undergoes stretched-helix transition, hydrophilically grafted chains may form loops.
Figure 2 Surface pressure-area isotherms at air-water interface at 25 C for hydrophilically modified silicones compared with PDMS.
The superimposed isotherms of hydrophilically modified silicones and PDMS (figure 2) shows that the curves are almost the same upto 120Å2/repeat unit (i.e. in regions I and II), with slight differences possibly due to minor variations in the equivalent weights of respective polymers. This is proposed to be due to stretched conformation of chains in regions I and II, where only chain lengths play an important role and not the functional groups. On further compression, between 120Å2/repeat unit and 50Å2/repeat unit, the chain undergoes a transition from stretched conformation to helical or loop structure. In this process some of the functional groups are pulled or removed out of water. The functional group that interacts most strongly with water will offer maximum resistance to come out of water surface. Hence the chain having higher affinity for water undergoes higher compression and shows higher surface pressure. Based on this hypothesis, the slope of the curves in region III can be considered to be a measure of the hydrophilicity of the functional groups on the chain. A gradation in hydrophilicity of modified silicones at air-water interface has been predicted based on the langmuir isotherm and correlation with the scaling theory. According to scaling theory, the increasing gradation of affinity of functional groups for water is
AMS>QMS>IMS>PDMS. Similar
trends have been reported in the past for end functionalized silicone
chains.
(1) Hill, R.M., Silicone surfactants; Surfactant science series.
Marcel Dekker: New York, 1996. 86.
(2) Hill, R.M., Silicone (siloxane) surfactants. In Encyclopedia
of physical science and technology 3rd ed.;R. A. Meyers, Ed. Academic
press: San Diego, CA 2002. 14: p. 793.
(3) E. D. Goddard, K.P.A., and P. Chandar, Silicone "superwetters".
Langmuir, 1995. 11: p. 1415.
(4) Steven A. Snow, W.N.F., and Michael J. Owen, Synthesis and characterization
of zwitterionic silicone sulfobetaine surfactants. Langmuir, 1990.
6: p. 385-391.
(5) Banks, W.H., Surface films of polydimethylsiloxanes on organic
liquid substrates. Nature, 1954. 174: p. 365-366.
Abstract for SPE meeting, April 22-26, 2006 Tulsa OK
Paper proposal for the Fifteenth SPE Improved Oil Recovery Symposium
Mineral wettability control by optimizing adsorption of mixed surfactants
S. Lu and P. Somasundaran
Columbia University, New York
Abstract
Reagent adsorption on reservoir minerals is one of the most
critical parameters in chemical flooding for improved oil recovery
both due to their depletion and changes in mineral wettability leading
to loss in sweep efficiency. The mechanisms that control both the
extent of adsorption and the nature of the nanostructure of the
adsorbed layer on relevant minerals were investigated in this work
using mixtures of a series of surfactants of different charge and
structure (nonionic alkyl ethoxylates, environmentally benign dodecyl-ß-D-maltoside
(DM), anionic sodium dodecyl sulfonate and cationic single chain
and Gemini amines) under various conditions of pH, salinity and,
most importantly, mixing ratio of the surfactants. To elucidate
the mechanisms involved, hydrophobicity of alumina particles was
also monitored along with the charge of the particles and interfacial
tension. It was discovered in this work that adsorption can be better
controlled for maximum increase or reduction by using a mixture
with one surfactant as an active adsorbate and the other as passive.
For example while both DM and Sulfonate surfactants are active on
alumina at pH 7 with maximum adsorption of both, interestingly only
the Sulfonate component is active at pH 4 and the other component
active at pH 10. It is proposed that the active species act as "anchors"
for passive molecules to adsorb at pH10 due to hydrophobic chain-chain
interaction but with the hydrophilic head groups oriented toward
the bulk solution, making the mineral water wetted at lower bulk
concentrations. On the basis of these results, it is proposed that
active/passive systems with a low fraction of active component can
be chosen to minimize adsorption and maximize the performance of
surfactants in surfactant flooding.
Abstract for SPE meeting, April 22-26, 2006 Tulsa OK
Nano-structure of Mixed Surfactant Aggregates in Solution and on Minerals
R. Zhang and P. Somasundaran
Columbia University, New York
Abstract
Enhanced Oil Recovery techniques are aimed towards attracting
the residual oil trapped in the reservoirs in the form of microdroplets
between sand particles or inside porous rocks using, for example,
by flooding with micellar solutions. Surfactants/polymers can change
the wettability of the rock markedly and thus keep mobilizing the
entrapped droplets. Since the nanostructures of the aggregates of
surfactant mixtures determine particularly the orientation of the
species, wettability as well as viscosity and the interfacial tension
and thus the efficiency of the EOR process, it is useful to monitor
the aggregates. The system of nonionic surfactant mixtures of n-dodecyl-ß-D-maltoside
(DM) and nonyl phenol ethoxylated decyl ether (NP-10) were investigated
in this work to indentify the role of the chemical structures of
the surfactants in determining the natures of aggregates and the
resultant surface modification of minerals. Using analytical ultracentrifuge
technique coexistence of two types of micelles was discovered in
solution of nonyl phenol ethoxylated decyl ether and its mixtures
with n-dodecyl-ß-D-maltoside while only one micellar type
was observed is present in n-dodecyl-ß-D-maltoside solutions.
One type of micelles was spherical while the other was elongated.In
the case of adsorption on minerals, interestingly NP-10 independently
adsorbs on silica and DM only coadsorbs through hydrophobic chain
chain interactions, while the role of each is reversed for the case
of adsorption on alumina. For the case of mixtures, a modified packing
parameter is proposed for predicting the formation of aggregates.
The structures are spherical or cylindrical on silica but those
on alumina undergo a spherical-to-cylindrical-to-bilayer transition
with increasing concentration of the primary adsorbent. The maximum
adsorption of the nonionic surfactant mixtures is determined by
the size of hydrophilic groups of both surfactants and, importantly,
the mixing ratio. This information enables tuning the formulations
of the chemical floods for better sweep efficiency by varying parameters
such as type of surfactants, molecular structures, mixing ratio
as well as the total concentration.
3-D and side views of various nanostructures together with the V/Vfull
ratio.
Abstract for SPE meeting, April 22-26, 2006 Tulsa OK
Conformational Behavior of Hydrophobically Modified Polymers and its Effect on the Stability of Emulsions and mineral wettability.
P. Somasundaran. T. Wines and P. Deo
Abstract
Hybrid polymers constitute a novel class of polymers that are
finding important applications in rheological control, enhanced
oil recovery, detergency, pharmaceuticals, paint and coating, etc,
owing to their unique structural combination of both surfactants
and polyelectrolytes. They form hydrophobic or hydrophilic nanodomains
depending upon the environment in a manner similar to surfactants,
but differing with respect to the size, shape, hydrophobicity/hydrophilicity
of the internal core, etc. This unique property, together with the
conformational sensitivity to pH, ionic strength and temperature,
gives hybrids additional opportunities in rheological control, improved
oil recovery and effluent treatment. In the current work, the solution
and solid/liquid interfacial properties of poly
(maleic acid/octyl vinyl ether) (PMAOVE) has been investigated by
studying hydrophobic aggregation, adsorption on solids and colloid
stability using a multi pronged experimental approach. The flexible
hydrophobic chains on
PMAOVE enable the polymer to form intra-molecular nanodomains in
solutions as detected by pyrene fluorescence with the nature of
the inside
nanodomain packing depending ,among other, on the solution pH.
Interestingly, the hypercoiled conformation of PMAOVE reduces its
parking area at the alumina/water interface and thus shows a higher
adsorption density than its unmodified homologue with the conformation
sensitivity to pH also exhibited by its interfacial adsorption behavior.
The effect of the hydrophobically modified polymer PMAOVE on the
solution behavior of reverse microemulsions studied using electrical
percolation, dynamic light scattering and electron spin resonance
techniques made them useful for controlling the reverse microemulsion
phase stability. These findings are expected to assist control of
the solution and interfacial properties of flooding fluids and design
of optimal additives in enhanced oil recovery schemes
Investigation of the Mobility of Amphiphilic Polymer - AOTReverse Microemulsion Systems Using Electron Spin Resonance
Thomas H. Wines; P. Somasundaran; Nichola J. Turro; Steffen
Jockusch; M. Francesca Ottaviani
NSF Industry/University Cooperative Research Center for Advanced
Studies in Novel Surfactants, Columbia University, NewYork, NY,
10027, USA
Abstract
Amphiphilic polymers can be used as tools to manipulate the
behavior of reverse microemulsions. EPR spectroscopy employing the
spin probe 5-doxyl stearic acid was used to study the adsorption
of a comb type polymer (polymaleic anhydride octyl vinyl ether)
and a di-block polymer (polybutadiene-ethylene oxide) onto reverse
microemulsion droplets formed from Aerosol-OT/ heptane/water. The
findings indicate that the comb type polymer was adsorbed by the
reverse microemulsion drops at low polymer concentrations causing
a structural change of the micelle.
SPECTROSCOPIC INSIGHT INTO SURFACTANT-POLYMER INTERACTOINS IN SOLUTION AND AT SOLID LIQUID INTERFACES
P. Somasundaran
NSF Industry/University Cooperative Research Center for Advanced
Studies in Novel Surfactants, Columbia University, NewYork, NY,
10027, USA
Abstract
Polymers and surfactants have applications in a variety of
processes involving dispersion/flocculation, rheology control, deposition
and coating, solubilization, encapsulation/release etc. In addition
to adsorption density, the structure of the adsorbed layers determines
the interfacial properties of particles in these systems. In this
talk, the role of adsorbed layer nanostructural properties, namely
nano-polarity, nano-fluidity and most importantly molecular conformation
and orientation at solid-liquid interfaces in controlling the above
interfacial processes will be discussed. A multi-pronged approach
involving fluorescence, ESR, NMR, Resonance Raman and CAT Scan techniques,
along with conventional techniques to measure turbidity, settling,
surface charge and hydrophobicity was used to explore the adsorption
mechanism and the structure of the adsorbed layers. The suspension
stability and particles wettability display significant changes
concomitant with changes in the structure of the adsorbed layer.
When polymers are used, their conformation can be manipulated by
changing solution conditions such as pH and/or by the addition of
a second reagent. Such manipulation of polymer, particularly hybrid
polymers can be used to obtain desired levels of stabilization or
deposition of hydrophobic or hydrophilic particles.
The adsorption isotherms of surfactants on solids in aqueous show two to four different regions corresponding to different adsorption mechanisms. The colloidal properties also display significant changes concomitant with changes in the structure of the adsorbed layer. By changing the nature of solid surface, solution conditions or structure of the surfactant/polymer, adsorption as well as conformation of the adsorbed layer can be controlled. Such manipulation can lead to flocculation or dispersion even at the SAME adsorption density. Even the so called low molecular weight dispersants can act as good flocculants under appropriate dosage conditions. Controlling the adsorbed layers for desired performance will be discussed in this talk.
A bombardier beetle squirting benzoquinone poison or a "touch
me not" plant folding up rapidly upon being attacked are examples
of nanostructures in nature that provide inspiration for developing
new classes of nanomaterials. Such materials can effectively meet
the ever-increasing demand for reliable drug. In this talk, applications
of these nanomaterials will be explored following a discussion of
methods we have developed for producing and monitoring various nanostructures.
ROLE OF INTERACTIONS BETWEEN POLYMERS, SURFACTANTS AND PROTEINS IN MODIFYING SURFACES
P. Somasundaran
NSF Industry/University Cooperative Research Center for Advanced
Studies in Novel Surfactants, Columbia University, NewYork, NY,
10027, USA
Abstract
A bombardier beetle squirting benzoquinone poison or a "touch
me not" plant folding up rapidly upon being attacked or a lotus
leaf rolling off water beads are examples of nanostructures in nature
that provide inspiration for developing new classes of nanomaterials.
In this talk, applications of such nanostructures for control of
wettability, flocculation/dispersion, deposition, solubilization
and biosurface modification will be explored following a discussion
of methods developed for monitoring surfactant/polymer/protein aggregates
in solutions and at solid/liquid interfaces. Techniques used include
both spectroscopic techniques (fluorescence, ESR, NMR, Resonance
Raman, surface plasmon resonance), advanced analytical (Analytical
ultracentrifuge, ultrafiltration), scattering (neutron, light) techniques
along with conventional techniques used to measure turbidity, surface
charge and hydrophobicity.
In all cases, in addition to adsorption density, the nanostructure
of the adsorbed layer determines the interfacial properties of particles
in these systems. Thus depending on the orientation of the adsorbed
species, flocculation or dispersion of suspensions can be obtained
at the same polymer adsorption density and hydrophobicity or hydrophylicity
of surfaces can be obtained at the same adsorption density of surfactant
or hydrophobically modified polymers. In general while the wettability
changes of particles correlate with hemimicellization of surfactants
on them, stability of suspensions correlate with conformational
changes of adsorbed polymers and proteins on surfaces. In this talk
the role of nanostructure of adsorbed surfactant/polymer/protein
layers in controlling various interfacial phenomena and techniques
for obtaining desired colloidal performance will be discussed.
Controlled Dynamics of Poly(acrylic acid) Nanobrushes with Changes in pH, Ionic Strength and Time
Jing Wang, P. Somasundaran
NSF Industry/University Cooperative Research Center for Advanced
Studies in Novel Surfactants, Columbia University, NewYork, NY,
10027, USA
Abstract
Poly(acrylic acid) nanobrushes were prepared on polystyrene-coated
glass substrates via physisorption, and a number of techniques (Langmuir-Blodgett
technique, X-ray photoelectron spectroscopy, water contact angle
measurement, atomic force microscopy) were used to prepare and characterize
the brushes. Contact angle measurements showed the polystyrene-coated
glass surface to become more hydrophilic after poly(acrylic acid)
grafting on it. XPS results confirmed the presence of PAA on the
topmost surface of the substrate. From the results of AFM topographic
imaging of the surface of PAA brush on PS-coated glass substrate,
PAA brushes was found to form bigger and less densely distributed
aggregates on the surface with a decrease in the grafting density.
Also, PAA brush aggregates were found to undergo marked reversible
conformational changes from coiled to stretched and vice-versa with
changes in pH, ionic strength and contact time.
Complexations of poly(vinylcaprolactam) with anionic surfactants:
impact of surfactant molecular structures
Rui Zhang, Qiong Zhou, Larry Senak &
P. Somasundaran
Langmuir Center for Colloids and Interfaces
Columbia University, New York, N.Y. 10027
Abstract
Hydrophobically modified (HM) polymers with low consulate temperatures
(LCST) have advantages over conventional polymers for certain applications
as they display the behaviors of both surfactants and polymers.
The poly(vinylcaprolactam) (PVCAP) has been characterized and its
interactions with three anionic surfactants of various molecular
structures, i.e., dodecyl sulfonate (C12SO3), sodium bis(2-ethylhexyl)
sulfosuccinate (AOT) and disodium laureth 3 sulfosuccinate (SLE3)
at air/solution interfaces and in aqueous solutions at neutral pH,
have been studied in this work by measuring properties such as the
surface activity, the phase behavior, and the binding cooperativity.
At the air/aqueous solution interface, PVCAP participates in the
monolayer formation of C12SO3 and AOT while no such behavior is
observed for SLE3. Similarly in solution, PVCAP is found to interact
with AOT and C12SO3, surprisingly, not with SLE3. The ion-dipole
interaction is proposed to be the driving force to initiate the
complexation for
the first two combinations at cac. Both the three EO groups and
two charges in head group are responsible for the lack of reactivity
for PVCAP-SLE3. At concentration above cac, the aggregation number
of polymer-surfactant complex obtained from the binding isotherm
follows the order of AOT < C12SO3 < SLE3. The results are
interpreted with respect to surfactant molecular structures, such
as the charge density and inorganic-organic balance. It is expected
to tune the interaction of polymer and surfactant and obtain the
desired performance.
Aggregate formation of binary nonionic surfactant mixtures on
hydrophilic surfaces
R. Zhang
Langmuir Center for Colloids and Interfaces
Columbia University, New York, N.Y. 10027
Abstract
Adsorption of surfactant mixtures on hydrophilic solid surfaces
is of considerable theoretical and practical importance. Interestingly,
in this study, cooperative adsorption of nonionic surfactant mixtures
of nonyl phenol ethoxylated decyl ether (NP-10) and n-dodecyl-â-D-maltoside
(DM) on silica and alumina has been investigated with a view to
elucidate the nanostructures of their aggregates. In the mixed adsorption
process, DM is identified to be the "active" component
and NP is the "passive" one in the process of adsorption
on alumina, while their roles are reversed on silica. Strong interaction
between the surfactant molecules has been found for adsorption of
surfactant mixtures on silica but weak effect is observed for the
adsorption on alumina. The difference in the adsorptive interactions
of the surfactants with the above minerals is attributed to the
affinity of the active component to the solid surface and to the
differences in the molecular structures of the surfactants. To better
understand the interaction between surfactants at solid/solution
interface from a molecular structure point of view, the nanostructures
of mixed surface aggregates have been quantitatively predicted for
the first time using a modified packing index. This work is expected
to bringforth new sight to the understanding of structure-performance
relationship.
Study of mixtures of n-dodecyl-ß-D-maltoside with anionic, cationic and nonionic surfactant in aqueous solutions using surface tension and fluorescence techniques
R. Zhang, L. Zhang, & P. Somasundaran
Langmuir Center for Colloids and Interfaces
Columbia University, New York, N.Y. 10027
Journal of Colloid and Interface Science, Volume 278, Issue 2,
15 October 2004, Pages 453-460
Abstract
Surfactants of practical interest are invariably mixtures of
different types. In this study, mixtures of sugar-based n-dodecyl-ß-D-maltoside
with cationic dodecyltrimethylammonium bromide, anionic sodium dodecylsulfate
and nonionic pentaethyleneglycol monododecyl ether in solution,
with and without supporting electrolyte, have been studied using
surface tension and fluorescence spectroscopic techniques. Interaction
parameters and mole fraction of components in mixed micelles were
calculated using regular solution theory. The magnitude of interactions
between n-dodecyl-ß-D-maltoside with other surfactants followed
an order anionic/nonionic > cationic/nonionic > nonionic/nonionic
mixtures. Since all surfactants have the same hydrophobic groups,
strengths of interactions are attributed to the structures of hydrophilic
headgroups. Electrolyte reduced synergism between n-dodecyl-ß-D-maltoside
and ionic surfactant due to charge neutralization. Industrial sugar-based
surfactant, dodecyl polyglucoside, yielded results similar to that
by dodecyl maltoside, implying that tested commercial alkyl polyglucosides
are similar to the pure laboratory samples in synergistic interactions
with other surfactants. Fluorescence study not only supported the
cmc results using tensiometry, but showed that interfaces of all
the above mixed micelles/water are mildly hydrophobic. Based on
these results, an attempt is made to discover the nature of interactions
to be a combination of intermolecular potential energies, free energy
due to packing of surfactant molecules in micelles.
Abnormal Micellar Growth in Sugar-based and Ethoxylated Nonionic Surfactants and Their mixtures in Dilute Regimes Using Analytical Ultracentrifugation
R. Zhang & P. Somasundaran
Langmuir Center for Colloids and Interfaces
Columbia University, New York, N.Y. 10027
Langmuir; (Article); 2004; ASAP Article; DOI: 10.1021/la049295a
Abstract
In order to develop structure-property relationships for surfactants
that control their adsorption, solubilization and micellization
behavior in mixed systems, and to develop predictive models based
on such relationships, it is necessary to acquire quantitative information
on various species present in these complex systems. Analytical
ultracentrifugation technique is selected for the first time to
characterize the species present in mixed micellar solutions due
to its powerful ability to separate particles based on their size
and shape. Two nonionic surfactants, n-dodecyl-ß-D-maltoside
(DM) and nonyl phenol ethoxylated decyl ether (NP-10), and their
1:1 molar ratio mixtures were investigated in this study. Micelles
of the nonionic surfactants and their mixtures are asymmetrical
in shape at cmc. Interestingly, unlike ionic surfactants, the micellar
growths of the nonionic surfactants were found to occur at concentration
immediately above the cmc. The results from both sedimentation velocity
and sedimentation equilibrium experiments suggest coexistence of
two types of micelles in nonyl phenol ethoxylated decyl ether solutions
and its mixtures with n-dodecyl-ß-D-maltoside while only one
micellar species is present in n-dodecyl-ß-D-maltoside solutions.
Type I micelles were primary micelles at cmc while type II micelles
were elongated micelles. The differences in the micellar shapes
of n-dodecyl-ß-D-maltoside and nonyl phenol ethoxylated decyl
ether are attributed to packing parameters detected by their molecular
structures.
Novel Nanogels for Encapsulation and Slow Release of Personal Care Actives
S. Chakraborty, P. Somasundaran & C. Gryte
NSF Industry/University Cooperative Center in Novel Surfactants
Columbia University, New York, NY 10025
Abstract
In personal care industries, it is a crucial problem to incorporate
water-incompatible perfume molecules in reliable carriers and to
release them at desired rates and desired sites. Nanogels are a
type of spherical, covalently crosslinked polymeric networks with
the particle size in nanometer range which can effectively encapsulate
such materials. Since nanogels are small, porous and can swell/shrink
in different environments and can be functionalized, they are potential
carriers for fragrance and antimicrobial agents.
Nanogels were synthesized in this work by inverse microemulsion
polymerization and by systematic modification, a series of functional
nanogels, (hydrophobic nanogels, ionic nanogels and dually modified
nanogels with both hydrophobic and ionic groups), were generated.
Small molecule encapsulation experiments were carried out with these
nanogels to determine the effects of functionalization. The nanogels
chemically modified for hydrophobicity and electrostatic charge
showed markedly higher ability for small molecule extraction as
compared to the unmodified nanogels. In saline, although the efficiency
of all types of nanogels was decreased, the hydrophobic nanogels
showed much better performance than other types of nanogels. The
range and capacity of the nanogels could be controlled by determining
the effects of these functional groups on their loading properties.
Mechanisms by which the functional groups influence the small molecule
extraction are explored.
ENVIRONMENTALLY BENIGN SURFACTANTS FOR EFFICIENT ENHANCED OIL RECOVERYP.
Somasundaran and Q. Zhou
National Science Foundation I/UCR Center for Novel Surfactants
Langmuir Center for Colloids and Interfaces
Columbia University, New York, NY
Abstract
A large amount of oil is trapped in reservoirs made up of porous
rocks after the traditional oil production. Various chemical methods
have been under development to recover this oil, but they have been
less than satisfactory due to the high cost of chemicals as well
their loss by adsorption on reservoir rocks and precipitation. Indeed
potential contamination of the environment by the chemicals is also
a new important element to be considered. Thus there is a dire need
to develop cost effective efficient environmentally benign chemicals
to increase the recovery from oil reservoirs.
New surfactants capable of tolerating harsh conditions created by
extremes of pH, temperature or inorganics and capable of interacting
favorably with the polymers are promising in this regard. Such surfactants
as sugar based ones and pyrrolidones are attracting attention, as
they are potentially biodegradable. In many cases, mixed surfactants
perform much better than single surfactants due to synergetic effects
and ability to alleviate precipitation. Importantly, the effect
of surfactants depend not only how much is adsorbed but also how
they adsorb. A water wetted rock surface that is beneficial for
displacement of oil can be obtained by manipulating the orientation
of the adsorbed layers. Availability of modern equipment such as
analytical ultracentrifuge, fluorescence and electron spin resonance
spectrophotometers offers an unprecedented opportunity for elucidating
the mechanisms involved and for designing optimum processes.
In this paper, problems and strategies for environmentally benign
schemes for surfactants and polymers for improved oil recovery are
considered. Some new schemes for coal cleaning based on the same
principles are also briefly mentioned. Finally, opportunities for
collaboration between the United States and Chinese researchers
using their synthesis and analytical capabilities are indicated.
An EPR Investigation of the Adsorption of Dendrimers on Porous Surfaces
M. Francesca Ottaviani, Nicholas J. Turro,
Steffen Jockusch, Donald A. Tomalia
Abstract
Guest-host interactions of poly(amidoamine) dendrimers and porous
surfaces, such as homoporous silica of different pore sizes, activated
alumina (acidic, neutral, basic), and MCM-41 zeolite (Si/Al=30)
were investigated by electron paramagnetic resonance (EPR) spectroscopy.
Two generations of dendrimers were selected, G2 and G6, representing
“early” and“late” generations, which were
labeled with a nitroxide radical. It was found that the main
parameters regulating the adsorption and interaction of the dendrimers
and porous surfaces are: (I) the size of the pores of the porous
materials (host) relative to the size of the dendrimer (guest),
(II) the total surface area of the host that is accessible to the
guest dendrimers, and (III) the chemical composition of the host
and guest surfaces that come into contact upon adsorption.
If the pore size of the host surface is smaller than the guest dendrimer
diameter, then adsorption of the dendrimer occurs exclusively on
the external host surface. If the pore size of the host surface
is bigger than the dendrimer diameter, then the internal surface
area is accessible to the dendrimers and large amounts of dendrimers
are adsorbed. The chemical composition of the host surface
and guest surface determines the strength of the host-guest interaction.
An increase in alumina content (silica < zeolite MCM-41 <
alumina) of the host increased the electrostatic interaction of
the dendrimer with the host surface. Increased protonation
of the external dendrimer amino groups also increased the electrostatic
interaction. For the large dendrimers (G6), which possess
a closed surface structure, electrostatic interactions are the main
forces of host-guest interaction. Therefore, the strongest
interaction of G6 was observed with basic alumina. For small
dendrimers (G2), which possess an open structure, hydrophobic interactions
between the low polarity internal dendrimer structure and the low
polarity Si-O-Si groups of the host surface provide an additional
host-guest interaction. High protonation of the dendrimer
surface and high alumina content of the host surface inhibits this
hydrophobic type of interactions. The combination of low polar
Si-O-Si groups and highly polar AlO- groups in the zeolite MCM-41
probably cause the strongest interaction of the guest G2 dendrimer
with MCM-41 compared to the other investigated host surfaces.
Polymer Adsorption and Conformation inDispersion/Flocculation of Concentrated Suspensions
Zhonghua Pan, P. Somasundaran
NSF Industry/University Cooperative Research Center for Advanced
Studies in Novel Surfactants, Langmuir Center for Colloids and Interfaces
Columbia University, New York, N Y 10027
Abstract
Performance of polymers as stabilizers or flocculants for controlling
the properties of concentrated suspensions depends upon the extent
of the polymer adsorption as well as conformation at solid-liquid
interfaces. Solids loading, polymer molecular weight and fractionation,
and dissolved solid species, are important factors that control
the polymer adsorption and conformation and the system behavior.
In this study, polymer molecular weight fractionation and adsorption
changes were monitored using stepwise adsorption tests and polydispersed
polymer samples with techniques such as TOC (total organic carbon)
and GPC (gel-permeation chromatography). Fluorescence and ESR (electron
spin resonance) spectroscopy were used to explore the conformation/orientation
of the polymers adsorbed on solid. Aluminum concentration of
the residual solutions was determined using ICP (inductively coupled
plasma) atomic emission. To investigate effects of dissolved alumina
species on the system behavior, zeta potential measurements of the
suspensions were made using a Zeta-Meter Model D.
It was found that the adsorption of PAA on alumina did not change
significantly with increase in solids loading from 2 vol. % to 15
vol. %. Our earlier studies showed a “greater”adsorption
density at low solids loading and a marked decrease in adsorption
with increase in solids loading in the same range. Interestingly,
it was found that the polymer adsorption behavior at high solids
loading is different from that at low solids loading when the polymer
sample contains impurity such as dioxane. Under the test conditions,
smaller polymer molecules were found to preferentially adsorb first
at the interfaces. Polymer molecular weight fractionation due to
such preferential adsorption is more evident at low solids loading
than at high solids loading, suggesting an increasing effect of
particle-particle interaction on polymer diffusion. Concentration
of the dissolved alumina species in the residual solutions was found
to increase significantly as the system becomes denser, and this
in turn affects the conformation of PAA in the solution: PAA
molecules become more coiled in the presence of the dissolved alumina
species at pH<7 even though the concentration of the species
is low. Zeta potential of PAA-alumina suspensions with addition
of dissolved alumina species was found to be markedly higher than
that of PAA-alumina systems in the range of pH 4 to pH 10, suggesting
that alumina surface becomes more positive in this pH range
possibly due to increasing complexation of PAA with the dissolved
alumina species.
Preliminary results of fluorescence and ESR spectra in our earlier
studies suggested that the adsorbed PAA molecules tend to stretch
out or dangle more into the solution as the system becomes denser.
It is very clear that monodispersed polymer samples with fluorescence
and spin labels are required to monitor the polymer conformation.
More control experiments are also needed to monitor and minimize
the effects of the labels on the system behavior.
Polyacrylic acid adsorption and conformation in concentrated alumina suspensions
Zhonghua Pan, Adrian Campbell, P. Somasundaran
NSF Industry/University Cooperative Research for Advanced Studies
in Novel Surfactants
Langmuir Center for Colloids and Interfaces
Columbia University, New York, 10027, U.S.A.
Abstract
Particulate suspensions used in many industrial processes are typically
highly concentrated and it is often difficult to keep them well
dispersed or flocculated. Polymer adsorption is usually employed
to achieve desired colloidal and rheological properties of such
suspensions. In this work, adsorption of polyacrylic acid (PAA)
in concentrated alumina dispersion has been monitored to determine
the effect of solids loading on both the adsorption as well as the
conformation of the adsorbed species. Fluorescence and electron
spin resonance (ESR) spectroscopy were used to determine the conformation
of labeled PAA adsorbed on alumina particles. Solids loading were
found to have interesting effects on PAA adsorption and conformation
at the alumina-water interface. As the solids loading is increased,
the adsorption density of PAA was found to decrease under conditions
of a fixed high initial polymer concentration. However, in the case
of adsorption using reduced initial polymer concentration, this
solid loading dependence was removed. Conformational studies (conducted
at a constant adsorption density) showed the polymer molecules to
become more stretched with increasing solids loading. The relationship
between the polymer conformation and the particle dispersion was
also investigated. Stretching of the adsorbed polymer was found
in this case to produce an increase in the settling rate obtained,
suggesting bridging effects.
Complexation between poly(maleic acid/octyl vinyl ether) and poly(vinyl caprolactam) in aqueous solution and at alumina/water interface
Q. Qiu and P. Somasundaran*
Langmuir Center for Colloids and Interfaces
Columbia University
520 West 120th Street, Room 911, New York, NY 10027
Abstract
Solution and interfacial properties of binary polymer mixtures of
poly(maleic acid/octyl vinyl ether) (PMAOVE) and poly(vinyl caprolactam)
(PVCAP) have been studied for the alumina/water system. To test
the hydrophobic effect, mixtures of poly(maleic acid/methyl vinyl
ether) (PMAMVE) and PVCAP is also investigated and compared to the
behavior of PMAOVE/PVCAP. At low pH, both polymer mixtures become
turbid upon mixing. The turbidity increases at low mixing ratios
of PVCAP to the vinyl ether component, reaches a maximum and then
decreases at higher mixing ratios. Upon shifting the pH to the alkaline
range, i.e pH 7.5 and above, the turbid solution becomes clear for
both the polymer mixtures. Cloud point measurements indicate absence
of complexation of PVCAP with PMAMVE under the alkaline conditions,
but strong interaction with PMAOVE. This is attributed to the different
forces involved in the complexation among the polymers: H-bonding
for PVCAP/PMAMVE, and both H-bonding and hydrophobic effects for
PVCAP/PMAOVE. At alumina/water interface, the normally non-adsorbing
PVCAP is triggered to adsorb by PMAOVE, attributed to the hydrophobic
complexation between the two. However, the adsorption of PVCAP shows
a maximum as a function of the concentration of PMAOVE. At concentrations
of PMAOVE above the onset of its own plateau adsorption, the amount
of PVCAP triggered to adsorb is reduced possibly due to the polymer
complex formation in solution.
Hydrophobic Complexation of Poly(vinyl caprolactam) With Sodium Dodecylsulfate and Dodecyltrimethylammonium Bromide in Solution
Q.Qiu, P. Somasundaran, and B.A. Pethica
Langmuir Center for Colloids and Interfaces
Columbia University
500 West 120th Street, Room 911, New York, NY 10027
Abstract
The interaction of poly(vinyl caprolactam) (PVCAP) with sodium dodecylsulfate
(SDS) and dodecyltrimethylammonium bromide (DTAB) in aqueous solutions
has been studied systematically by measuring the phase separation
temperature, hydrodynamic radius, pyrene solubility, and surfactant
binding isotherms. Both surfactants were observed to elevate the
solution cloud point of PVCAP and cause the polymer to undergo a
coil to globule transition. This transition occurs at a concentration
about a tenth of the critical micelle concentration (cmc) for SDS
in the absence of polymer, but at the cmc with DTAB. The results
indicate that PVCAP interacts with SDS monomers, but only
with micelles in the case of DTAB. The phase behavior of the PVCAP/SDS/DTAB
ternary system shows that the binding of SDS to PVCAP is reversible
on changing the concentration of the free surfactant monomer in
solution. Potentiometric titration of PVCAP solution and pyrene
solubility in its mixtures with surfactants suggest that complexation
of PVCAP and SDS is due to a combination of ion-dipole and hydrophobic
effects. PVCAP and DTAB micelles interact through hydrophobic inclusion
of polymer segments into the DTAB micelles. Pyrene is not solubilized
by PVCAP in solution alone. Addition of SDS to PVCAP solutions induces
marked pyrene solubilization well below the cmc, characterized by
a region indicating saturation adsorption of the pyrene to the PVCAP/SDS
complex. Above the SDS cmc solubilization of pyrene increases linearly
with SDS concentration, corresponding to inclusion of the pyrene
into the SDS micelles. In contrast to SDS, the addition of DTAB
to a solution of PVCAP shows no pyrene solubilization until the
cmc is reached.
Removal of Arsenic Species by the flotation of Ions
Zhonghua Pan, Lei Zhang and P. Somasundaran
NSF Industry/University Cooperative Research Center for Advanced
Studies in Novel Surfactants, Langmuir Center for Colloids and Interfaces,
Columbia University, New York, NY 10027, U.S.A.
Abstract
Foam Flotation, a relatively inexpensive technique, has been employed
for the first time for enhanced removal of arsenic species from
the solution. This method involves interactions between arsenic
species and surfactants and removal of hydrophobic complexes formed
by air bubbles under quiescent conditions. The system in our experiments
consists of Arsenic (V) oxide hydrate, dodecylamine (CH3(CH2)11NH2),
pyrogallol (C6H3(OH)3), or sodium dodecyl sulfate (CH3(CH2)11OSO3Na)
aluminum chloride, and others. It was found that as much as 98%
removal of arsenic species can be obtained, the removal being dependent
upon the solution pH and the interactions between As species and
surfactants used as activators or collectors. These results suggest
that foam flotation based on the interactions between As species
and surfactants is a new effective method either by itself or in
combination with other techniques for the removal of As species
from the solution.
International Synopisum of Arsenic in Drinking Water
November 26-27, Columbia University
Cyclic Voltammetric Study of Redox Reactions of Arsenic
Z.Wei, P. Duby, P. Somasundaran
Many treatment technologies are capable of removing arsenic from
potable water. So far, adsorption of Arsenic (III and IV) by oxides
of Aluminum, Iron and their mixtures has shown encouraging results.
The present study is to provide the fundamental knowledge of the
oxidation or reduction between arsenic species in water for further
development of treatment techniques.
The redox reactions between As(III) and As(V) in acidic solution
were investigated using cyclic voltammetric technique with a Pt
rotating disk electrode (RDE). In the potential region corresponding
to the reduction or oxidation of arsenic species only one cathodic
and one anodic peak were observed, indicating that the redox reactions
between As(III) and As(V) are controlled by one slow reaction, although
two electrons are transferred. Judged by the shift of the peak potential
when changing scan rate and the distance between anodic peak potential
and cathodic peak potential, the redox reactions between As(III)
and As(V) are irreversible slow reactions. Digital simulation will
be employed to obtain kinetic information of the reactions.
Physicochemical Interactions In Arsenic Remediation: A Study Using Atomic Force Microscopy
D. Sarkar and P. Somasundaran
Abstract
Many treatment technologies are capable of removing arsenic from
potable water, but the socio-economic situation of the affected
region complicates the choice of treatment technologies. So far,
adsorption of Arsenic (III and IV) by oxides of aluminum, iron and
their mixtures has shown encouraging results. We are working to
understand the basic interaction mechanism of arsenic species with
such surfaces, using atomic force microscopy.
We investigated the deposition of arsenic species on glass surfaces,
activated by ferric ions, after activation by ferric oxide particles
failed to provide any evidence of arsenic deposition. With background
knowledge that iron activates oxide minerals for adsorption of surfactant
only in the pH window of 2 to 4, a monolayer adsorption of iron
was attempted at pH 3.50. Such monolayer adsorption made it possible
to study the interfacial processes by AFM. Initial results, does
show deposition of the arsenic species on the glass surface, as
sharp jagged precipitates.
Overcoming Contamination in Surface Plasmon Resonance Spectroscopy
D. Sarkar
Abstract
Surface plasmon resonance spectroscopy is a technique used for detection
of subtle changes in the optical properties of materials, and finds
wide application in biosensors and chemical tranducers. Due to the
extreme sensitivity, contamination of the sensor surface is a major
problem in experiments involving surface plasmon resonance spectroscopy.
We report here that aluminum oxide (alumina) can be used as a perfect
protective coating for the metal in surface plasmon resonance experiments.
The alumina is electron beam evaporated to create a relatively thick
layer on the sensor (gold) surface, immediately after the gold deposition
process without exposing the latter to environmental conditions.
During experiment, this protective coating was removed by dissolving
the alumina in an alkaline solution, thus exposing the nascent,
un-contaminated gold surface for further experiments. By studying
the shift in the waveguide modes supported in the dielectric alumina
layer, the dissolution of alumina was monitored. Theoretical simulation
studies using Fresnel’s equations were done to explain the
dissolution plots obtained. Atomic force microscopy of the alumina
surface provided information on the variation of the roughness parameter,
with the progress in dissolution. It was found that the roughness
of the surface at all points during the dissolution process remained
much below the wavelength of the incident radiation, thus justifying
the modeling of the system as stacked Fresnel’s layers.
Conformational Dynamics of Polyacrylic Acid;
A Study Using Surface Plasmon Resonance Spectroscopy
D. Sarkar
Abstract
The conformational dynamics of polyacrylic acid induced by pH change
is reported here. Polyacrylic acid immobilized on gold surface was
exposed to pH changes and the conformational changes thus induced
were followed in real time using surface plasmon resonance spectroscopy.
The temporal profile of the stretching-coiling phenomenon showed
an inflexion point, which was proposed to be arising due to the
contradictory behavior of two different property changes in the
polymeric system. Normally SPR response would be a convoluted effect
of the thickness and refractive index changes, but the behavior
observed here where the SPR response is predominantly governed by
either one of the two, is unique and to the author’s knowledge
is a feature, which is observed for the first time. Analysis of
the kinetics of the angle change revealed that it takes longer for
the polymer to stretch than it takes for it to collapse, with the
kinetic rate constants varying by at least an order of magnitude.
The SPR angle change as well as the kinetic constants increased
linearly with molecular weight. Effect of Ca2+ was studied and it
was found that the polymer was locked in its conformation due to
the binding of this multivalent cations.
Polymer Surfactant Kinetics Using Surface Plasmon Resonance Spectroscopy
Dodecyltrimethylammonium
Chloride / Polyacrylic Acid System
D. Sarkar
Abstract
Kinetics of polymer surfactant interactions and the effect of surfactant
binding on the conformational dynamics of the polymer were explored
in this work using surface plasmon resonance spectroscopy. Polyacrylic
acid (PAA) was modified with thiol to varying degrees so as to force
the polymer to form different loop sizes upon adsorption on the
gold SPR sensor surface. Dodecyltrimethylammonium Chloride (DTAC)
in solution was flowed over the polymer coated sensor surface and
the binding was followed in real time. It was found that control
of the loop size of the polymer on the solid surface enabled in
turn the control of surfactant binding, with the largest loop allowing
the maximum amount of surfactant to bind and vice versa. The kinetic
plot of the binding showed three distinct segments. The first segment
followed convective-diffusive kinetics. The second and third segments
followed first order kinetics with the second rate being significantly
faster than the first one. Careful analysis of the second segment
showed that it is possible to divide it into two different segments,
each following a first-order kinetics, with the second rate being
slightly slower than the first one suggesting a gradual slow down
of the reaction due to convolution from the polymer conformational
changes. Mechanistically, the sudden increase in the rate for the
third segment of surfactant binding implies that the polymer matrix
is opening up so as to incorporate more surfactant molecules. This
was attributed to the formation of charged double surfactant species
the repulsive interaction in which prevented the polymer network
from imploding. Studies using unmodified polymers suggested the
possibility of sudden conformational rearrangement in the polymer
network, with progress in surfactant binding. Furthermore, the reflectance
of the SPR spectrum was found to increase upon surfactant binding
implying that there is a decreased efficiency of coupling of the
incident radiation into the surface plasmon mode of the metal, which
suggested that the surfactant actually penetrated the polymer matrix.
Interfacial Dynamics of Macromolecules Using
Surface Plasmon Resonance Spectroscopy
D. Sarkar
Thesis Abstract
This thesis reports an in situ study of the conformational dynamics
of polymers under external perturbation, using surface plasmon resonance
spectroscopy. The research was undertaken to follow the response
of stimulated macromolecules as the understanding of the basic interactions
governing such, and the ability to gain control on the time evolution
of three-dimensional structures is fundamental in developing smart
materials of the future. SPR is a surface sensitive technique providing
easy route to perturb a molecule and follow its relaxation in real
time. As part of this research work a surface plasmon resonance
spectroscope has been developed and the use of aluminum oxide (alumina)
as a protective coating for the sensor surface has been reported
for the first time.
The main aim of this project is to follow the conformational dynamics
of macromolecules at solid/liquid interface. Polyacrylic acid (PAA)
was chosen as the primary target molecule because of its chemistry
and vast known literature. Response of immobilized PAA to changes
in pH was followed in real time and the results correlated to the
changing electrostatics of the system. The changing predominance
of property changes governing the SPR response gave rise to an inflexion
point, which to the author’s knowledge was observed for the
first time. Interestingly, kinetic rate constants suggested that
it takes longer for the polymer to stretch, than it takes for it
to coil back, which was attributed to the decrease in local pH and
the impermeability of the hydroxyl ions through the coiled polymer
layer.
A second perturbation to the polyacrylic acid system was in the
form of cationic surfactant (dodecyltrimethylammonium chloride)
molecules. It was found that the amount of surfactant binding was
directly proportional to the loop size of the polymer on the solid
surface, which was controlled by modifying the polymer to varying
degrees of thiolation. The temporal profile suggested the opening
up of the polymer matrix due to the development of repulsive interactions,
thus providing novel information on the conformational evolution
of the polymer structure over time.
