Chemistry and Physics of Polymeric Nanostructured Materials

Our research focuses on nanostructured polymers with the aim of opening up new areas of applications and to clarify the relevant science in the field. For many practical applications of these nanostructures, it is necessary to know the conditions that lead to the formation of a certain structure in the nanometer range. We are interested in block copolymer based nanoscopic structures (both in bulk and thin films) formed by self-assembly/supramolecular assembly, the influence of changing conditions on the formation of the microstructure and the ability to control these processes. 

In bulk, we mainly focus on the block copolymers containing crystallizable blocks. The introduction of crystallizable blocks in block copolymers control the solid-state structure and generate fascinating morphologies due to the complex interplay between microphase separation and crystallization. For example, the structural evolution of poly(ʟ-lactide) (PLLA) during heating of the amorphous ABA triblock copolymers was demonstrated. We are also interested in the block copolymer based supramolecular assemblies (SMA), which are produced by the association of small organic molecules with one of the polymer blocks by noncovalent interaction such as hydrogen bonding, electrostatic interactions, π-π interactions, etc. SMA possesses versatile opportunities to introduce various functionalities and properties of small molecular additives to solution processable block copolymers.

In thin films, we are interested in understanding the factors that control the orientation of block copolymer microdomains and also the mechanism of orientational changes of microdomains formed in block copolymer thin films.

Block Copolymers

Biodegradable Polymers

We are also interested in the development of biodegradable nanocomposites using hexagonal boron nitride (h-BN) and understanding the structure development of PLLA in the presence of highly dispersed pristine and functionalized h-BN nanosheets. 

The presence of an asymmetric carbon in the polylactide backbone causes the chirality in molecules, and the polymer chain adopts the helical conformation. We are also interested in designing the helical architectures using block copolymers containing PLLA as one of the blocks and star-shaped polymers with PLLA as arms. 

Poly(ʟ-lactide) (PLLA) is a 100 % biodegradable thermoplastic of bio-origin, and it has become a competitive commodity material to petroleum-based thermoplastics over the past decades. PLLA being a commodity plastic used to make fibres and packaging films, it is used in biomedical implants, surgical sutures, and bone fixation devices. One of the major drawbacks of PLLA is its poor crystallization rate and low crystallinity. Our group is interested in understanding the structure-formation mechanism in biodegradable polymers and their impact on material properties. 

The solvent-specific competition between solvent-induced crystallization and dissolution in PLLA control the crystal structure and crystallinity of the polymer. We are interested in understanding the molecular, crystalline and lamellar structure of PLLA in different solvent environments.

Polymer-based nanocomposites filled with nanosized stiff particles have evolved and attracted great interests from both industry and academia during the last two decades. Performance of polymer nanocomposites strongly depends on the degree of dispersion and aspect ratio of layered materials in the polymer matrices. In particular, exfoliation of layered materials in polymer matrices has been shown to improve the flame retardancy, optical, thermal, rheological and mechanical properties of the base polymer.

Our group mainly focuses on the synthetic clays, i.e., layered double hydroxides (LDH) expressed by the general formula [M1-x2+Mx3+(OH)2]x+Ax/mn-nH2O (where M2+, M3+, and An- represent divalent metal cation, trivalent metal cation and interlayer anions, respectively). We have developed novel methods for the successful preparation of highly dispersed nanocomposites using wide varieties of LDH. We have been systematically investigated the effect of the lateral size of LDH on the crystallization behavior and thermal stability of host polymers.

We have demonstrated that the proper selection of metal constituents of LDH is imperative in the preparation of polymer/LDH nanocomposites with desirable properties. The thermal stability and flame retardant properties of the iPP nanocomposite containing three-metal-LDH is superior to nanocomposites made with the two-metal-LDH.

Low dielectric (low κ) materials are of crucial significance in the field of electronic packaging applications and substrate applications as well. In order to achieve low dielectric constant, two strategies were mainly adopted: either decrease the number of dipoles or decrease the dipole strength. Decreasing the number of dipoles in an ILD (interlayer dielectric) can be achieved by effectively reducing the density of the material, which is practically materialized by the introduction of additional porosity. Incorporation of air in the dense material will lead to the decreased dielectric constant. Our group, in collaboration with Dr. K.P. Surendran, developed new strategies to reduce the dielectric constant of polymers using nanocomposites technology.

Polymer Nanocomposites

Polymer Aerogels

Development of polymeric aerogels has been attracted the researchers from both academia and industry, as these materials have extremely low density with the combination of the excellent thermal insulation and useful mechanical properties. Polymeric aerogels with ample mechanical strength whose density and porosity are comparable to the traditional inorganic aerogels promoted the utilization of porous scaffolds in diverse fields like thermal and acoustic insulations, capacitors, oil adsorbents, etc. We have been using the freeze-drying technique to obtain highly porous polymer aerogels. Freeze-drying has got several advantages in the preparation of aerogels over the other techniques such as supercritical drying since this is a simple, cost-effective and widely available technique. Here there is no size limitation for the sample, and also the use of supercritical fluids is eliminated. We used ethanol and water for the solvent exchange before carrying out the freeze drying, and the method is easily scalable and environment-friendly. 

Natural Fibres based Composites

Among various natural fibres produced in India, coconut fibre, commonly known as coir, has the shortest renewable time and stands next to jute fibre in production. India accounts for more than two-thirds of the world production of coir and coir products. Kerala is the home of Indian coir industry, particularly white fibre, accounting for 61 % of coconut production and over 85 % of coir products. Coir has been used for creating environment-friendly products such as mattresses, geotextiles, construction of roads, horticulture, buildings, etc. Recent advances in the field of composite technology paved development of new coir-based products for the commercial exploitation and diversification of its applications. Over the past several years, CSIR-NIIST has been working in the area of coir fibre composites that acquired unique knowledge, expertise and developed products targeted processes. Attempts have also been made to conduct field trials and produce products which could attract end users

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