La von Duddleson Krumb Professor
 Director, IUCRC for Advanced Studies in Novel Surfactants
Director, Langmuir Center for Colloids and Interfaces
Columbia University, New York, N.Y. 10027
Phone: (212) 854-2926
FAX: (212) 854-8362
E-mail: ps24@columbia.edu




Research Interests


Research Interests

Green Surfactants and Their Interfacial Properties

With the advantage of environmental compatibility, the demand for green surfactants has been steadily increasing and they may eventually replace their chemically synthesized counterparts. Generally, the surface active reagents that are produced from renewable resources or bioprocesses and are environmentally friendly are considered to be green surfactants. For instance sugar-based polyglucosides and protein based surfactants have been applied in some industrial areas. These green surfactants have many advantages, such as biodegradability, low toxicity and environmental compatibility and have amphiphatic properties since their complex structures are composed of hydrophilic and hydrophobic portions. For further understanding on green surfactants, their interfacial properties have to been investigated in the comparison with conventional petroleum based surfactants. So far, several green model surfactants including sugar based maltoside, sophorolipid and lipopeptides have been investigated using techniques like surface tension, fluorescence spectroscopic, total organic carbon analysis techniques. These surfactants have shown unique interfacial properties such as high selective adsorption on solids which can be applied for mineral separation. It is our major aim to understand the unique behavior such as adsorption, as well as their structure-property-performance relationship.

Selective Adsorption of n-Dodecyl-β-D-Maltoside on Solids





Mixed Surfactant Systems: Sugar-based surfactants in Mixtures

The project objective is to investigate interfacial phenomena such as adsorption, solubilization and micellization behavior of mixed surfactant systems and to explore the synergistic effects of novel surfactant mixtures to reduce the carbon footprint due to surfactant applications. Sugar-based surfactants are environmentally benign and have unique solution and interfacial properties. Gemini surfactants with two hydrophobic and two hydrophilic groups show more pronounced interfacial and solution properties.  These surfactants have potential use in a wide variety of applications. The goal is to elucidate mechanisms governing solution and interfacial behavior of the mixed systems and the role of structural variations, and to generate a database for novel applications.  Adsorption of nonionic / Gemini surfactant mixtures and nonionic / nonionic surfactant mixtures is studied.  Analytical ultracentrifugation technique is employed for the first time to investigate the surfactant mixtures in solutions. Interestingly, unlike ionic surfactants, the micellar growths of DM and NP-10 surfactants and their mixtures were found to occur at concentrations immediately above the cmc. The results suggest coexistence of different types of micelles in NP-10 solutions and its mixtures with sugar-based surfactant while only one micellar species is present in sugar-based surfactant solutions. This technique is powerful for distinguishing the size and shape of various species in mixtures. Besides, both dynamic and equilibrium characteristics of microemulsion, nanoparticles, microgel for drug-delivery, polymer-surfactant and surfactant mixtures can be obtained using this technique.

Evaluation of Hydrophobicity of Nanoparticles and Correlation with Their Toxicity on Nitrosomonas Europaea

        Nanotechnology has many applications but toxicity of nanoparticles has become of increasing concern in recent times.  Recent research shows that depending on their surface chemistry, size, surface area, crystallinity and surface charge, nanoparticles can produce toxicity on cells via different mechanisms.  In this work, we focus on developing techniques to monitor hydrophobicity/wettability and to correlate it with toxicity. Since traditional techniques are not quite valid at the nano level, we have developed a new technique based on measuring trace water adsorption to quantitatively evaluate the hydrophobicity of the nanoparticles. This technique is able to yield surface energy values for different types of nanoparticles and values correlated with the effects on Nitrosomonas Europaea bacteria cell morphology (X. Fang, B.Li, I. Chernyshova, P. Somasundaran, “Ranking of as received micro/nano particles by their surface energy Values at Ambient Conditions”, Journal of Physical Chemistry C, in print).


Dispersion/ Aggregation of nanoparticles in Water



Novel Polymeric Nanoparticles for Extraction and Release of Drugs and Fragrance

Nanoparticles are finding increasing applications as effective drug/attribute delivery devices. Previously, we have successfully designed modified poly(acrylamide) nanoparticles for overdose drug toxic extraction. The objective of the current project is to synthesize poly(acrylic acid) and other polymeric nanoparticles for incorporating fragrances and antimicrobial agents into the nanoparticles and study their subsequent release from the matrix. Novel polyacrylamide and poly(acrylic acid) nanoparticles (50-100 nm) have been synthesized by the reverse microemulsion method.  The polyacrylamide nanoparticles after modification with charged and hydrophobic groups showed overdosed drug (amitriptyline)  extraction of 80% compared to 18% for unmodified nanoparticles. The extraction of the fragrance, linalyl acetate by the nanoparticles were recently studied. It was observed that 1% crosslinked poly(acrylic acid) nanoparticles could incorporate 38% of the linalyl acetate added to the system in 4 hours. The efficacy of extraction increased when these nanoparticles were further modified with hydrophobic moieties like propyl amine and hexyl amine.  Potential of poly(acryl amide) nanoparticles to extract  vanillin by was also studied.  When the release profile of incorporated linalyl acetate was monitored as a function of pH of the dispersion media, it was observed that the release was pH dependent.  The potential of these nanoparticles for extraction of drugs like amitriptyline and bupivacaine is also being  investigated. Surface Plasmon Resonance(SPR) technique is being used to investigate short term extraction and release. 



Toxicity of Nanoparticles and their Interaction with Lipid Vesicles in Micro-Fluidic Device














The rising number of applications of nanoparticles (NPs) in commercial and consumer product industry, biological sciences and medical diagnostics have drawn attention on the hazards NPs pose to human health and environment. However, the biomolecular mechanisms of NPs’ toxicity have not been fully elucidated due to the complication of diverse properties of nanoparticles and composition of cells.

The cell membrane is a thin layer of phospholipids-cholesterol mixture which contain liquid ordered phase (Lo), liquid disordered phase (Ld) as well as gel phases (s). Different type of membrane proteins was believed to partition into special phases. Those proteins play a very important role in many cell membrane functions, such as mediating endocytosis, sorting in polarized epithelial cells, virus budding, and immune receptor signaling. NPs with different properties (i.e., size, charge) are proposed to show preferential partition into the membrane phases, which physically or chemically interfere with the protein associated process and therefore will impair cell’s normal functionalities.  Both model membrane and cell plasma membrane are to be used as the study objectives targeted by the functionalized NPs. The as produced giant unilamellar vesicles (liposome) will be microfluidically arrayed intact on a surface for in-situ fluorescence interrogation and following interaction with nanoparticles. The aim of this project is to establish a relationship between the interactions of functionalized NPs with functional microdomains such as rafts on a model cell membrane, and to determine how the surface properties of NPs will affect such relationships. The results can help us to better understand the cytotoxicity of NPs in-vitro.









Interactions between Commercial Detergent Enzyme and Green Bio-Surfactants

Detergents in traditional washing machines rely on high temperatures and vigorous agitation in order to remove stains, which can contain a mixture of proteins, starches and lipids along with inorganic components. By using enzymes, the organic components in soiled fabrics can be broken down into smaller, easily soluble fragments and removed at lower temperatures with less mechanical energy and water consumption. However, the enzymes currently being used in most current commercial formulations are fairly non-specific; combining a variety of enzymes capable of hydrolyzing a wide range of organic compounds. Considering that green surfactants also comprise of sugar or peptide base units there exists the strong possibility of these compounds demonstrating antagonistic interactions with the detergent enzymes, diminishing the overall effectiveness of the newly introduced bio-surfactant, enzyme or both and presenting a potentially significant hurdle in universally applying green surfactants in commercial applications.

While the general goal of the project is to identify this possible hurdle in the commercialization of green surfactants, the analytical approaches to this project will focus on understanding three fundamental aspects of the enzyme/surfactant interactions. 1) NMR, FTIR and HPLC to characterize the surfactant before and after introduction to the enzyme. 2) Florescence, Dynamic Light Scattering and Ultra centrifugation to observe the surfactant micelle formation while interacting with enzymes and 3) Surface tension measurements to study the surface activity of enzyme affected surfactants. 4) Enzyme activity tests: to understand the effects of bio-surfactants on enzymatic activity.


michael's picture



A Fundamental Study of Nanoparticle–Protein Mutual Interactions: Role of Nanoparticle Morphology and Size

The lack of fundamental knowledge on the effects of nanoparticulate morphology on nanoparticle (NP)–protein interactions greatly limits our understanding of the behavior of NPs in biological systems. Correlation between  physico-chemical properties of nanomaterials (e.g., particle size, shape,  nano-roughness/porosity, surface energy, crystallinity, surface charge, structure of adsorption sites, hydrophobicity) and  their interactions with different biomolecules they may come in contact during natural  and man-made processes will allow for better modeling, predicting, and designing capabilities of  nanomaterials. This project is the first phase of a fundamental systematic study of the effects of  nanomorphological properties of NPs and micron-size nanopatterned particles on NP-protein and NP-cell interactions. Understanding the fundamental mechanisms that govern the adsorption processes in competitive biological environments will help to find ways to control NPs performance as additives in cosmetics and house hold products, drug delivery, bioimaging, medical device coatings, bio-sensors, biochip development, biofouling protection, and nanotoxicology amongt others.

A unique feature of this research is the molecular-level spectroscopic as well as nanoscale local characterization of the adsorption process. These include forces between the NP and protein, the adsorption mode of the protein, evolution of the NP morphology, aggregation state, and size upon interacting with the protein. This objective will be achieved by adapting existing characterization and measurement tools, especially spectroscopic techniques such as Raman and FTIR Spectroscopy in conjunction with extensive quantum chemistry modeling and by developing new methodologies.









Solution and Interfacial Behavior of Hydrophobically Modified Polymers

Hybrid modified polymers have features of both polymers and surfactants. Due to the associative nature of the hydrophobic groups, hybrid polymer can form intra-molecular as well as inter-molecular aggregates. This project aims to explore the adsorption, solubilization and turbidity properties of hydrophobically modified polymers in solutions along with their relevant colloidal applications. The association behavior, the major characteristic of hybrid polymers, is addressed with respect to their structure.  Currently the interaction of several hybrid polymer surfactants such as poly(maleic acid/octyl viny ether) (PMAOVE) with sodium dodecyl sulfate (SDS) is studied. The ESR spectrum of 5-doxyl stearic acid (5-DSA), a probe molecule, indicates immobilization of the probe molecule in the hydrophobic nanodomains of the polymer in SDS-free solution.  A sharp increase in the mobility of the probe was observed at around 2.2 mM  and 8mM of SDS suggesting the structural reorientation of PMAOVE and formation of mixed micelles of PMAOVE and SDS,. Upon further addition of SDS, the mobility of the probe remains constant, implying coexistence of SDS micelles and mixed micelles of PMAOVE and SDS. Such coexistence has major implications in their performances in colloidal processes. 



Interfacial Behavior of Hydrophilically Modified Silicone Surfactants

Siloxane based materials have become very important in industrial processes because of their unique properties in both aqueous and non-aqueous systems. Among them, a special class of hydrophilically modified molecules is termed silicone surfactants.  These surfactants are commonly used as mold release agents, PU foam stabilizers, superspreaders for aqueous systems and emulsifiers in cosmetics.

We are investigating the interfacial characteristics of functionally grafted dimethylsiloxane backbone chains modified with various cationic, anionic, non-ionic and amphoteric functional groups.




To study the effect of functional groups on modified silicones the liquid-liquid interfacial properties, phase diagrams and rheology behaviors were monitored. Various modified polymers show markedly different emulsion stabilizing characteristics based on the hydrophilicity of functional moieties. Also viscosities of emulsions were observed to increase drastically due to interactions of functional groups in aqueous phase, and thus formation of loose networks among the siloxane backbones. The diagrams have been established to design formulations that would possess properties desired for a given application.


Modified Silicone Polymers and their Interactions with Fabric Substrates

Our current project, which examines the interactions between silicones and fabrics, is aimed towards designing optimum surfactants and process schemes. Our primary objective is to establish a relationship between substrate properties and the particle size and surface charge of silicone emulsions as a function of their chemical structure that are used to treat them. AFM was used as a tool to monitor the surface modification of fibers. It was observed that the treated fibers are far more smoothened, relaxed and uniform as compared to the untreated. Thus the morphology of the fabric is modified by treatment with specialty silicones. Furthermore, these results give a microscopic insight into the macroscopic properties such as softness and antiwrinkle of the silicone treated fabrics. FTIR and Raman studies of fibers were undertaken to understand the interactions of silicone polymers with fabric substrates. Raman has been employed to understand the stress-strain behavior of fabrics originating from different source materials or having undergone different treatments (H. Liem 2007, Eichhorn 2003). Raman band of C–O ring stretching mode at 1095 cm-1 shifts toward lower wavenumber during tensile deformation of fibers (shown in figure below). Magnitude of the shift depends upon the chemical structure, morphology, and microstructure of fibers. We observed lowering of stress from the Raman spectra of treated fibers i.e. a shift towards higher wavenumber suggesting relaxation of fibers.




Mineral Resource Recovery Programs: Fundamental and Applied Research, New Reagents and New Technology

Sustainability in the mineral industry is contingent upon converting resources to reserves. Overall, this is dictated by the ability to economically process difficult-to-treat ore bodies of base and precious metals such as Cu, Ni, Co, Zn, Au, and Platinum group metals.

While there are several complex factors which affect the value mineral separations from these ores, the two important factors that adversely affect the value of mineral recovery are slurry rheology and slime coating. The former is associated with the type and nature of the minerals and their morphologies, while the latter is related to the surface chemistry and electrostatic effects.

Given Columbia’s IUCRC expertise in fine particle processing and surface chemistry as well as Cytec Industries Inc’ leadership in reagent technology for mineral separations, new approaches and methodologies are being used to address these challenges and to develop novel reagents. Preliminary results have showed considerable improvements in the yield of value minerals, some of which are of strategic importance.

Furthermore, mineral morphology and its effects will also be studied. Green chemistry and greener processing methods will be attempted to alleviate environmental concerns. A fundamental understanding of complex mineral-reagent interactions on micro and nano scales will be developed through this collaborative research, thus helping mineral companies, such as Vale Inco and Newmont to make value added products. This program provides a fine example of how industry and university image001can collaborate to solve major problems in the industry and simultaneously achieve educational and scientific goals.








Illustration of complex mineral flotation process



Study of Conformations and Orientations of Polymers at Interfaces Using Molecular Dynamics Simulations

Many new simulation techniques such as Molecular Dynamics (MD), Dissipative Particle Dynamics (DPD), Coarse Grained Molecular Dynamics (CGMD) and Stochastic Rotation Dynamics (SRD) have been developed during the past few years to understand and predict molecular and mesoscale phenomena for systems such as polymers, colloids, and soft materials. A unique advantage of simulation methods is that molecular level details can be obtained about a given system for a particular application. We have initiated a program to utilize some of these simulation techniques to enhance our understanding of relevant problems such as adsorption, dispersion, and wetting etc. Aim of this program is twofold. The first objective is to understand the dynamics at atomic levels, which are difficult to characterize using experiments with an acceptable degree of confidence. The second aim is to explain the experimental findings through a rational modeling framework that is verifiable through subsequent simulations. For example, we have used Molecular Dynamics simulations using compass forcefield method to calculate the preferred conformations and orientations of hybrid silicone polymers at air-water interface as a function of nature of functional modifications and surface concentrations. At low concentrations, poly(dimethylsiloxane) was observed to be in a stretched conformation, whereas acid and amino modified siloxane preferred a serpentine shape. With an increase in concentration, all of the polymers oriented themselves in coiled conformations, with the ionic ones immersing deeper into the web such that the interactions among functional groups and water are maximized. Understanding the fundamental properties the proposed approach can help in tailoring the reagents for specific applications.


The Role of Surfactants and Polymers in Flocculation/Dispersion

        Flocculation/dispersion of particles for proper processing and/or performance in industry is a critical and difficult issue to deal with, particularly when the solids content is rather high. It is our objective to understand the fundamentals involved in controlling the stability of concentrated suspensions. Surfactants and polymers are added as stabilizers/flocculants in such systems. For polymers, the extent of adsorption and molecular conformation at the solid-liquid interface often determine their ability to perform properly. Foremost problem in this regard has been the difficulty in monitoring adsorption and particularly conformation in high solids loading suspensions.

At the Center, in-situ monitoring of polymer adsorption and conformation in concentrated suspensions has been achieved by adapting the spectroscopic techniques such as fluorescence and ESR. We conducted a series of adsorption tests to check the adsorption behavior of polymers at different solid concentration in suspensions. It is noted that polymer conformation is changing with increasing solids loading. This is possibly due to preferential adsorption as a function of solids concentration. Effect of molecular weight distribution is therefore being investigated in detail using stepwise adsorption tests. The adsorption results from these tests along with chromatographic analysis of supernatants suggest preferential adsorption of polymers from a polydispersed system. These recent results imply that preferential adsorption plays an important role in regulating suspension stability, and point out the significance of determining polymer adsorption and conformation. This in turn suggests possibilities for fine-tuning molecular weight distribution of additives in order to obtain desired dispersion characteristics.



Adhesive Interactions between Particles in Aqueous and Non-Aqueous Media: Role of Surface Modification

Adhesive force between particles is an important factor governing a number of phenomena involved in industrial processes.  Direct measurement of that force can facilitate elucidation of mechanisms controlling adhesion as well as the identification of how to modify surface layers for optimum adhesion between particles, but there are no adequate techniques available for exploring the behavior of the typical particles present in real life industrial systems. 

The objective of this project is to study molecular mechanisms of adhesive interactions between particles in dispersions. The study includes direct in-situ measurement of the adhesive forces between various particles and between particles and large surfaces. The behavior of adsorbed layers is being studied for different surfactant and polymer additives with particular emphasis on interaction time. Media effects are being examined to understand how different adsorbents modify contacts in different environments.

Finally, the general rules and guidelines for the designing of additives that will have the desired effects in any given system of particles and media will be developed.


A Study of Dispersion Phenomena Using Molecular Dynamics Simulations

Aggregation of particles is a ubiquitous phenomenon in mineral and material processing industries. Reagents adsorbed onto the surfaces of these particles can be used to prevent aggregation and assist in particle dispersion. Dispersion has beneficial applications in mineral processing, ceramics processing industries where the charge is kept dispersed (selectively or otherwise). In some cases, dispersion is unavoidable and detrimental, i.e. in the tar-sand industry; micro-emulsion of water-in-oil droplets laden with solid particles poses a major handicap in the oil-recovery and increase the cost of its production. When particle sizes reach nanometer levels their tendencies to aggregate are stronger. This problem is further complicated by the lack of clear quantitative methodology to estimate the degree of dispersion of these particles due to different reagents. Atomistic simulation techniques such as Molecular Dynamics (MD) offer an effective way of modeling and estimating the strength of reagent-particle interactions and their correlation with the dispersion. Consequently, two main objectives have been envisaged for this program. The first objective is to develop a correlation between dispersion and interaction energy of particle-reagent system. The second objective is to calculate transport properties such as viscosity, thermal conductivity etc..,. The above objectives will provide a direct means to evaluate and compare various reagents used in these studies through simple rheological experiments. A standard methodology for correlating the dispersion phenomena with interaction strength and reagent packing density would be established.  Furthermore, the study will aid in development of highly effective, novel dispersant for any given industrial condition, which can be tailored and developed at a very low cost. It is believed that the success in this program will significantly reduce the time spent in developing new reagents for industries such as ceramics processing, coating, polymer fillers, pharmaceuticals, health care, mineral processing etc,.

4CNT1_1W_b4Aggregation observed in Carbon nanotube (CNT)-water suspensions









Before Simulation














Interactions of Surfactants & Surfactant Mixtures with Model Membranes, Liposomes, Microbes, and Antimicrobial Agents

Surfactants are used as solubilizing and cleaning agents in the formulation of household and personal care products. For efficient and safe use of these surfactants, it is important to have knowledge about the mechanisms of their interactions with membrane proteins, lipids, and other components particular to human skin. That will enable us to develop a model and in turn to design the most suitable surfactant systems for specific applications. Information is being currently compiled for systems composed of surfactants, their mixtures, liposomes and proteins as well as ceramides that are components of such biomaterials as skin. Results of surface tension, ESR and fluorescence spectroscopy, viscosity, and mass spectroscopy showed solubilization of phosphatidic acid-phosphatidyl choline liposome by sodium dodecyl sulfate to be a process in which the phosphatidic acid exits first, forming the mixed micelles and destabilizing the liposomes.  It was discovered that while cholesterol stabilizes the liposomes, zein protein enhances their dissolution due to the binding of the SDS, unfolding and disrupting the regular packing of liposome components. Interestingly liposomes prepared with ceramide were found to be almost inert towards sodium dodecyl sulfate but again vulnerable in the presence of zein protein. Such infraction should prove useful for developing products that are effective but biologically benign.


Study of Reagent Adsorption Kinetics Dynamics Using Surface Plasmon Resonance Spectroscopy

Specific reagent adsorption is the basis of many applications in industries such as microelectronics, mineral processing, cosmetics and personal care. Though considerable work has been done to understand the role of physico-chemical parameters of reagents and their adsorption, much less has been done to understand the kinetic aspects.  In many processes the rate of the adsorption of the reagent is very important, for example in understanding the effects of various species on flotation behavior.

In our work we investigated the use of surface plasmon resonance spectroscopy (SPR) to study the dynamics of reagent adsorption on precious metals and their alloys on a short time scale (milliseconds).

From SPR analysis it was observed that reagents with different functional groups have distinctively different binding rates. The rate of deposition of each reagent was calculated from theoretical considerations to obtain the adsorption density of reagent as a function of time. The limiting slope of this adsorption density vs. time graph at almost zero time was used as a tool to compare the relative rates of adsorption. A quantitative ranking was given to reagent adsorption kinetics based on the comparison of these limiting slopes. Such information will help the understanding of the real-life dynamic situations in flotation operation.


Aptamer Based Chemosensory Transducers, Toxic Scavengers or Carrier Attributes

Nucleic acid aptamers are oligonucleotides of modest size (~15-100 nucleotides) that can bind to a particular ligand with great affinity and selectivity. Ligands can range from metal ions to small organic molecules to proteins to viruses and even to bacterial cells. Aptamers are created and selected using a combination of synthetic chemistry, enzymology and interfacial chemistry involving affinity chromatography. Oligonucleotides not only have the ability to bind specific ligands, but also in some cases can catalyze a chemical reaction involving the ligand.  In these cases the ligand becomes a substrate.  A few RNA-based enzymes of this sort (ribozymes) exist in nature; for the most part these exhibit RNA-cleaving activity.  DNAzymes that cleave RNA or DNA at specific sequences have also been isolated through selection and amplification 


We propose here to develop aptamer-based biosensors in which ligand binding is coupled to the action of a protein enzyme to effect an amplification of several orders of magnitude. We start with a known DNAzyme with copper-dependent DNase activity; this DNAzyme is capable of self-cleavage at a specific resident single-stranded sequence. Amplification is effected by using this self-cleaving DNAzyme to tether a protein protease molecule to a solid support on one side of a small well.  Each time a copper ligand binds to a tether, it self-cleaves, releasing the protease.  Also present in the well is a short fluorescence probe connected to gold disks and embedded in a medium compatible with exposure to aqueous environments. The released protease diffuses to the gold disk and cleaves the peptides, releasing a fluorescent signal.