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Winner of the IUPAC Prize
for Young Chemists - 2000


Vijaya J. Patil
wins one of the first 4 IUPAC Prize for Young Chemists, for her Ph.D. thesis work entitled "Electrostatically controlled formation of nanocomposite thin films with organic matrices"

Current address (at the time of application)

Hindustan Lever Research Centre
64 - Main Road
Whitefields
Bangalore 560 066, India

Tel.: +91-80-8452959/1505
Fax: +91-80-8453086
E-mail: Bargaje.Vijaya@unilever.com

Academic degrees

  • Ph.D., National Chemical Laboratory, Pune, India
  • M. Sc., Department of Physics, University of Pune, India
  • B. Sc., D. G. Ruparel College, Bombay University, India

Ph.D. Thesis

Title Electrostatically Controlled Formation of Nanocomposite Thin Films with Organic Matrices
Adviser Dr. Murali Sastry
Thesis Committee Dr. Murali Sastry, Materials Chemistry Division, National Chemical Laboratory (NCL), Pune; Dr. Dominique Langevin, Laboratoire de Physique des solides, Universite Paris Sud, France; Dr. C. Manohar, Materials Chemistry Division, Bhaba Atomic Research Centre (BARC), Bombay; Dr. Ponarathnam, Polymers Chemistry Division, National Chemical Laboratory, Pune.

Essay

Developing techniques for synthesis and characterization of nanostructure have become a popular target and one of the grand challenges in materials synthesis. The remarkable, size-dependent physicochemical properties that nanoparticles can have, has fascinated and inspired the research activity in this direction. The techniques such as microlithography and deposition from the vapor that are extensively used to fabricate microstructures and devices require substantial efforts for extension to nanometer range. To meet this challenge, "engineering up" approach of synthesizing supramolecular assemblies, molecule by molecule to functioning electronic device taking cue from nature for use interplay of weak noncovalent bonding interactions, has become an increasingly attractive prospect. In this approach, nanoparticles play an important role of being building blocks of future nanostructures and organization of colloidal particles has been a subject of great interest, and is also the objective of this thesis. The kind of construction of nanocomposite thin films illustrated in my thesis work is essentially based on the use of non-covalent interactions for growing the thin films, which are self-synthesized.

In the work discussed in the thesis, repulsive electrostatic interactions were extensively used for stabilizing the colloidal particles and attractive electrostatic interactions between -NH3+ and -COO- was used to organize them. The motivation for the study was from the earlier work in our department on spontaneous organization of thermally evaporated fatty lipid films by an ion-exchange process. The fascinating part of this work was that such ion exchange leads to an organized lamellar film structure similar to c-axis oriented Y-type Langmuir Blodgett films. Recognizing that the principle of ion exchange is quite general, this approach has been extended to incorporate charged colloid into oppositely charged fatty lipid film in my thesis work.We have used the colloidal route, which is one of the most versatile methods for the synthesis of metal and semiconducting nanoparticles. The surface modification of colloidal particle surfaces was achieved using self-assembled monolayers of a bifunctional molecule which serves the dual purpose of electrostatically stabilizing the colloidal particles as well as providing a means of anchoring the particles to charged amphiphiles and organize them in fatty lipid matrix. Three dimensional self-assembly of n-alkane thiols and various other aspects of functionalization has been carried out rigorously in this work resulting in the first successful venture of exploiting hydrophobic interactions between the long chain fatty lipid molecules on the curved surface of clusters to form interdigitated bilayer structures. This strategy has been exploited to derivatize colloidal particles without the use of bifunctional molecules.

We have made a rigorous and successful attempt to organize colloidal particles in organic matrices to form nanocomposite thin films. It is shown that surface-modified colloidal particles can be viewed as "giant ions" and incorporated into thermally evaporated fatty lipid thin films by a simple immersion of the films in the colloidal solution. The cluster incorporation process is driven by the strength of attractive electrostatic interactions between the charged polar groups of the film matrix and the surface groups on the colloidal particles. Using various characterization techniques, it has been shown that the cluster density in the films can be controlled by simple variation of the colloidal solution pH. This is the only technique, which can demonstrate flexibility of controlling cluster density in organic matrix with simple variation of charge on the surface of clusters or the head-group of the fatty lipid by altering pH of colloidal solution. Also this is the unique technique to get very high volume fraction of colloids in nanocomposite, which is more than twice the values reported in literature till date.

Influence of colloidal particle concentration, particle size, solution pH as well as film thickness on the kinetics of cluster incorporation was obtained by quartz crystal microgravimetry (QCM) measurements. These results were discussed in terms of a one-dimensional (1-D) Fickian type diffusion model. It was found that 1-D diffusion adequately represents the cluster mass uptake kinetics observed using QCM, and an interesting film thickness and particle size dependence on the cluster diffusivity was observed. The applicability of this model to thermally evaporated films, leads to physically meaningful cluster concentration enhancements at the film-colloidal solution interface as well as cluster diffusivities. It is also observed that the cluster diffusivity increases as the cluster size is reduced. The pH at which maximum cluster incorporation occurs, is strongly dependent on the cluster size which is a very interesting result indicating that the nanoscale curvature influences strongly the ionization of the carboxylic acid groups in the monolayer surrounding the particles. The kinetics of cluster diffusion has also been studied using FTIR and in-situ and ex-situ UV-visible spectroscopies. FTIR spectroscopy is used to look at the fatty lipid matrix in the nanocomposite to understand coupling of the particles to the organic matrix and change in the orientation of hydrocarbon chains as clusters get incorporated. Whereas comparison of in-situ and ex-situ UV-Visible spectroscopy revels important information about swelling of organic matrix as a function of cluster size and solution pH and this information with FTIR studies gives a complete picture of the process of cluster diffusion in fatty lipid films. More than 30 different nanocomposites of various metal and semiconducting colloids of varying size with varying charge, in combination with corresponding fatty lipid organic matrix were systematically studied in the thesis work and role of specific parameters governing the film composition was thoroughly exploited.

Formation of nanocomposites of metal colloidal particles with surface derivatization using interdigitated bilayers was also studied in great detail as a part of my thesis work. It has been shown that facile incorporation of colloid with primary monolayer of octadecanethiol and secondary monolayer of carboxylic acid/amine can be achieved into thermally evaporated oppositely charged fatty lipid matrix. The advantage of using this approach is that it gives additional flexibility where varying the chain length of the secondary monolayer as well as the pH of the sol can monitor diffusivity and cluster density and eventual structure of the nanocomposite. The study on this novel technique of formation of nanocomposites was further continued through an investigation of the partitioning of carboxylic acid derivatized clusters of different sizes during a simultaneous incorporation process. It is observed that inspite of the larger diffusivities of the small colloidal particles, large particles are incorporated in the amine matrix. This "reverse" fractionation of the clusters was confirmed using Transmission Electron Microscopy and discussed in terms of an electrostatic model and the energetics of distortion of the amine matrix during cluster incorporation strongly supported by experimental and theoretical 1-Dimensional diffusion modeling data.

Recent developments in this field seem to indicate that future research will be directed towards the controlled design of both nanometer scale architectures and bulk materials built up from nanosized constituents. In this contest my thesis work where the novel concept of rationally assembling nanoparticles into organic matrix with intrinsic advantage of flexibility of controlling the cluster density is gaining significant importance. One of the most attractive prospects of this strategy is that technologically important, oxide and magnetic particles like TiO2, Fe3O4 can be organized using this technique and this work is currently been pursued in our lab. Our group has recently demonstrated that biologically important molecules like proteolytic enzime pepsin can be successfully encapsulated in the fatty lipid films. In addition to the above, well-defined superlattice structures can be obtained through alternate deposition of fatty lipid and incorporating different hydrosols which shows promise for obtaining alternating metal-semiconductor nanocomposites. We believe that, this technique has exciting potential for application in chemical and biological sensors, in addition to advanced materials with novel optical and electronic properties.


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