Events

Title: Self-Assembly of Amphiphilic Macromolecules and π -Conjugated Chromophores in Aqueous Medium

Abstract: In the recent past we have developed two distinctly different non-ionic amphiphilic systems which show spontaneous vesicular assembly in aqueous medium. The first one is based on amphiphilic random copolymers. Substitution of the N-hydroxysuccinimide group present in the parent copolymer by various hydrophobic amines generated a series of amphiphilic random copolymers in which the pendant non-ionic hydrophilic segments were attached to the polymer backbone by thermo-responsive amide group. Detail self-assembly studies revealed thermoresponsive vesicular assembly by all the polymers. Various parameters such as critical aggregation concentration, dye-loading capacity, particle size and lower critical solution temperature (LCST) of these vesicular assemblies could be tuned and co-related with the nature of the hydrophilic substitution or in other words the hydrophobic/hydrophilic balance of a particular polymer. At elevated temperature (beyond LCST), dehydration of the amide-backbone resulted in unprecedented vesicle-to-micelle transition and consequently thermo-responsive sustained release of encapsulated hydrophilic guest molecules could be achieved. The other system is based on a π - conjugated bolaamphiphile in which the central naphthalene-diimide (NDI) chromophore is attached to two nonionic hydrophilic wedges by a rigid linker containing self-complementary H bonding functionality. This showed spontaneous vesicle formation by synergistic effect of & π ;-stacking and hydrogen-bonding. Spectroscopic studies with the actual bolaamphiphile and related building blocks confirmed existence of H-bonding even in aqueous medium. Facile intercalation of pyrene and its derivatives could be noticed in the vesicular membrane owing to strong charge-transfer interaction among pyrene and NDI. Multifunctional vesicles could be prepared in situ by intercalating functional pyrene chromophores. In specific cases, such intercalation caused increase in radius of curvature of the mixed vesicle leading to morphology transition from 2D vesicle to 1D fiber which at higher concentration produced hydrogel. First part of the presentation will elaborate on recent advances in nano-structured assemblies of various amphiphilic systems from literature and their implications in biomedical applications. Later half of the talk will be focused on two specific amphiphilic systems developed in our groups as described above.

Date and Time: 12th April 2012, 2.30 pm

Venu: Shanti Swaroop Bhatnagar Lecture Theater in PMA Bldg 

Co-ordinator:

Dr. Suresh Bhat Scientist,

Complex Fluids & Polymer Engg. Group

Room No. J 105, Polymers & Advanced Materials Laboratory

National Chemical Laboratory, Pashan,

Pune, India Ph: +91-20-2590-2154

Abstract: Dielectrophoresis (DEP) is defined as the force exerted on a dielectric particle in a non-uniform electric Composite Materials non field. It can be used as a tool for precise on-chip colloidal manipulation and assembly and has been applied previously for making uniform structures from nano- and microparticles. We have extended the method of controlled on-chip DEP assembly to the making of permanent structures from live cells. Alternating electric fields applied across suspensions of cells such as baker’s baker s yeast and NIH/3T3 mouse fibroblasts are used to fabricate 1-D chains and 2-D arrays. The various operating parameters are optimized. The cells are further combined with  synthetic inorganic nano- and microparticles to yield ultimate “smart” materials. The particles are conjugated with lectins and attached to the cells irreversibly via biospecific lectin-polysaccharide interactions, thus, acting as biocolloidal binders between cells. The use of magnetic particles adds an additional functionality to the live cell 2- D matrix and we are able to manipulate the material in external magnetic fields. In summary, a simple technique is illustrated to synthesize novel permanent functional biocomposite materials. Applications of the new biocomposites include 1-D cell “wires” in bioelectronic circuitry or 2-D cell membranes in sensors, coatings, bioreactors and biomedical implants.

Date and Time: 16  th Febryary 2012, 4.00 pm

Venu: Shanti Swaroop Bhatnagar Lecture Theater in PMA Bldg 

Co-ordinator:

Dr. Suresh Bhat Scientist,

Complex Fluids & Polymer Engg. Group

Room No. J 105, Polymers & Advanced Materials Laboratory

National Chemical Laboratory, Pashan,

Pune, India Ph: +91-20-2590-2154

Title:  Polymer nanocomposites: Emerging trends and possibilities

Abstract:  Polymeric systems present us with a variety of behavior.  These highly entropic particles, exhibit unique physics and exhibit remarkable phenomena.  When micron to nanometer sized colloidal particles are added to a polymer melt, the mixture takes on added features of high mechanical and thermal stability.  A persistent question in the field of polymer nanocomposites is that of mixture stability.  The synthesis of new kinds of nanoparticles, have led to new possibilities for polymer nanocomposites.  Examples include chemically anisotropic colloidal particles which hold the promise of novel self-assembled systems, and carbon nanotubes which when dispersed in a polymer matrix may give rise to highly conducting systems.  This talk will focus on the next generation of polymer nanocomposites, and the questions associated with them.

Title: Tuning self-assembly of colloids – shape and solvent effects

Abstract:  Complex fluids and fluid interfaces containing particles, surfactants, polymers or their mixtures are ubiquitous in many consumer products and industrial nano-formulations. Several novel and advanced materials have been realized through tailoring of interactions between constituents, self-assembly, and flow induced microstructural changes in these complex fluid mixtures. These materials have received significant attention due to potential applications as – photonic materials, stabilization of emulsions and foams, templated synthesis, etc. In this talk, current activities on coffee ring effect and emulsion stabilization will be briefly discussed. For most part, talk will focus on two problems – self-assembly of anisotropic particles at fluid interfaces and self-assembly of surfactant molecules in ionic liquids.

Date and Time: 20  th October 2011, 4.00 pm

Venu: Shanti Swaroop Bhatnagar Lecture Theater in PMA Bldg 

Co-ordinator:

Dr. Suresh Bhat Scientist,

Complex Fluids & Polymer Engg. Group

Room No. J 105, Polymers & Advanced Materials Laboratory

National Chemical Laboratory, Pashan,

Pune, India Ph: +91-20-2590-2154

Title: Complex System behaviour of hydrotropes in mixtures with surfactants and their applications

Abstract: Hydrotropes, a group of small size amphiphiles, show a remarkable property of solubilizing other organic solutes in aqueous solutions which can be used to overcome solubility limitations for many otherwise heterogeneous reactions. Hydrotropes are also known to disrupt the liquid lamellar structure of surfactant assemblies and therefore have been used to permeabilise the cellular structures of plants in extraction of active ingredients from plant matrices.

Most remarkable is the viscoelastic behaviour of solutions of hydrotropes when combined with oppositely charged surfactants producing intermeshed living polymers. This behaviour is dependent on the charges on the head group as well as on the alkyl substituents on the aromatic ring. The molecular interactions between these components have been characterized by several techniques, including SANS and FTIR.

Date and Time:  15 th September 2011, 4.00 pm

Venu: Shanti Swaroop Bhatnagar Lecture Theater in PMA Bldg

Seminar Co-ordinator:

Dr. Suresh Bhat Scientist,

Complex Fluids & Polymer Engg. Group

Room No. J 105, Polymers & Advanced Materials Laboratory

National Chemical Laboratory, Pashan,

Pune, India Ph: +91-20-2590-2154

Title: Functional Nanomaterials by Self Assembly: Experiments, Mechanism, Modeling

Abstract:Technological requirements of advanced materials can be diverse, but the principles of self-assembly and surface chemistry can help us in designing materials with different geometry and functionality. For example, solid nanoparticles in general are required to be monodisperse and of controlled morphology. This has been achieved through confinement of reaction and resulting particle nucleation and growth within self-assembled reverse micelle cores, whereby we are able to synthesize and mathematically model nanoparticles. In contrast, simple switching of the reaction zone from inside to the external surface of the micelles eventually leads to synthesis of nanoporous materials. The latter can be further impregnated with different dispersed constituents (like nanoparticles, enzymes), or functionalized with chemical moieties. The resulting nanocomposite may be tailored for selective access of a guest species to the dispersed or functionalized component, enhancing overall performance. This will be illustrated by our results in photocatalysis, water treatment and enzyme activity. These are examples of complex multiphase systems, dominated by the presence of liquid-liquid or solid-liquid interfaces. In this talk, I will highlight both our experiments and models in trying to delineate the role of different microscopic interaction parameters and process variables, that determine the mechanism of formation and structure. Such an understanding of physicochemical phenomena over diverse time and length scales may eventually give us a complete description from molecular templates to material synthesis, structure and functionality.

Date and Time: 18  August 2011, 4:00 p.m.

Venu: Shanti Swaroop Bhatnagar Lecture Theater in PMA Bldg

Seminar Co-ordinator:

Title: Electrodynamic Manipulation of Electroneutral Materials

Abstract: According to Richard Feynman if history of mankind is written after ten thousand years the most significant event of the 19th century will be judged as the discovery of the laws of electrodynamics; everything else would pale in to insignificance. The mystery and potential of the electrodynamic forces continues to bewilder and spring surprises to us, even today. The application of these forces as means for manipulation of materials to create novel manmade-structures, is still in its infancy. While the action of electric fields on electrically charged objects is relatively better understood, the role of dilectrophoretic forces, even if they are being inadvertently deployed for an application, is not often well appreciated. The magnitude and direction of these forces is a complex function of the electric field vector, the gradient of the field, its frequency of oscillation, and the constitutive properties of the material being manipulated; which in turn, are a function of the impressed electric field. The presentation will give a brief and selective overview of the vast subject matter emerging in the area of preparing materials at molecular to meter scale, employing diverse material forms such as liquids or solid particles, and deploying electric fields from tens of volts to kilovolts, at sinusoidal frequencies from zero to tera hertz.

Date and Time: 21st July 2011, 4:00 p.m.

Venu: Shanti Swaroop Bhatanagar Lecture Theater in PAM Bldg

Seminar Co-ordinator:

Title: Microrheology during gelation: crosslinking reactions in poly(sodium acrylate)
Abstract:Liquid-solid transitions in the form of gelation are involved in various engineering examples, which include polymer processing, emulsions/paints application, food processing and petroleum processing. The gel point characterizes the transition from a liquid-like state to a solid-like state. This transition is usually associated with formation of percolating clusters in the material. The seminar will begin with an overview of gelation and rheological signatures near the gel point. In recent times, microrheology is being used to probe mechanical response of soft matter. Specifically, it is also being used to observe gelation, with the possible advantages of applying the technique to weak gels and/or heterogenous gels. After a brief introduction to the technique, the seminar will summarize our ongoing efforts to characterize gelation in crosslinking polymers.

Date and Time: 17th June 2011, 4:00 p.m.

Venue: Shanti Swaroop Bhatnagar Lecture Theater in PAM Bldg

Seminar Co-ordinator:

Dr. Suresh Bhat

Scientist, Complex Fluids & Polymer Engg. Group

Room No. J 105, Polymers & Advanced Materials Laboratory

National Chemical Laboratory, Pashan, Pune, India

Ph: +91-20-2590-2154 

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