Lakshmi Unnikrishnan

Polyethersulfone Membranes: The Effect of Sulfonation on the Properties

Polyethersulfone (PES) was sulfonated using chlorosulfonic acid in order to improve proton conductivity. Incorporation of ‒SO3H groups into polymer main chain through sulfonation was confirmed using FTIR and 1H NMR. Ion exchange capacity of sulfonated membranes was determined via titration. Morphological studies (AFM, SEM) revealed the presence of hydrophilic proton transfer channels, which became continuous at higher degrees of sulfonation. Thermal stability was observed from thermogravimetric analysis (TGA). Storage modulus and tan δ also exhibited an increase with degree of sulfonation as determined from DMA. Conductivity measurements and fuel cell performance showed that sulfonated samples possessed higher conductivity than virgin PES.

Polysulfone/C30B Nanocomposite Membranes for Fuel Cell Applications: Effect of Various Sulfonating Agents

The effect of various sulfonating agents (Chlorosulfonic acid and Trimethylsilylchlorosulfonate (TMSCS) on the performance of Polysulfone (PSU) nanocomposite membranes was investigated. FTIR and 1H NMR results confirmed the sulfonation reaction. Sulfonation of PSU as well as incorporation of Cloisite 30B (C30B) as a filler, resulted in an increase of proton conductivity, water uptake and glass transition temperature (Tg). Thermogravimetric analysis (TGA) exhibited a decrease in decomposition temperature with sulfonation.XRD confirmed positive interaction between C30B and SPSU. Surface and cross-sectional morphology of the membranes were studied using SEM.

Proton exchange membranes from sulfonated poly(ether ether ketone) reinforced with silica nanoparticles

The feasibility of sulfonated poly(ether ether ketone) (SPEEK) membranes reinforced with unmodified silica (SiO2) and modified silica (SiO2–SO3H) nanoparticles as proton exchange membranes (PEMs) was investigated here. The sulfonated membranes were characterized for degree of sulfonation, thermal stability, as well as water/methanol uptake properties. The incorporation of SiO2 increased the hydrophilic behavior thus allowing more water retention, which facilitated an easy pathway for proton transfer. However, a reduction in proton conductivity was observed. The strong –SO3H/–SO3H interaction between SPEEK chains and SiO2–SO3H led to ionic cross-linking in the membrane structure, which compensated for this decrement in proton conductivity. The fuel cell performance study revealed the potential of SPEEK/SiO2–SO3H nanocomposite membrane to act as an efficient PEM for fuel cell application.

Effect of nanofillers on selectivity of high performance mixed matrix membranes for separating gas mixtures

Techniques for separation of gas mixtures obtained from various sources, such as effluents from industries, and biogas, have always fascinated researchers. The advent of mixed matrix membranes (MMMs) has opened up a new window of opportunity for developing membranes coupled with flexibility, processability, and permeability of polymers and selectivity of inorganic nanomaterials. This review is a detailed overview of the effect of various nanofillers on the separation performance of MMMs including the major factors affecting the perm-selectivity and possible solutions for overcoming the emerging challenges. The paper also presents contemporary approaches for cost-effective implementation of MMMs. Methodologies for designing MMMs with improved interfacial morphology to exploit their full potential in tailoring the selectivity efficiency are also discussed in detail. This review can act be a guideline for the future development of high-performance MMMs for industrial applications without compromising long-term separation performance, durability, and stability to processing conditions.

Structurally modified aromatic sulfone polymer nanocomposites as polyelectrolyte membranes

A candid approach to analyze the prospects of organic–inorganic nanocomposites as polyelectrolytes has been presented in this communication. Structurally modified aromatic sulfone polymer, polysulfone, was successfully prepared through modification with trimethyl silyl chlorosulfonate, which was confirmed from Fourier transform infrared spectrographs. Different classes of nanofillers like layered silicates and inorganic oxides were reinforced in the modified macromolecular system using solvent casting technique. A comparative study was performed to evaluate the effectiveness of filled polyelectrolyte membranes in a direct methanol fuel cell operated at 60°C with 1.0 M methanol feed. Atomic force micrographs revealed the phase morphology, responsible for this behaviour. The variation in ion transfer behavior as a function of structural modification and filler composition was also conducted. Furthermore, supportive information for these characterizations were derived from morphological (x-ray diffractometry), thermal (thermogravimetric analysis), and liquid uptake studies.

Hybridization of MWCNTs and reduced graphene oxide on random and electrically aligned nanocomposite membrane for selective separation of O2/N2 gas pair

This present study demonstrates the development of high-performance polysulfone (PSf) hybrid mixed matrix membranes (MMMs) through the collaborative inclusion of multiwalled carbon nanotubes (CNTs) and reduced graphene oxide (rGO). The nanofillers are aligned by virtue of an AC electric field in order to formulate a multifunctional composite membrane structure for selective separation of O2/N2 gas. Proper alignment of the conducting nanofillers within PSf was confirmed by utilizing different microscopy and spectroscopy techniques. Hybridization of CNTS and rGO resulted in concurrent enhancement of permeability as well as the selectivity of the neat membrane. The inclusion of rGO nanosheets established a long, tortuous path hindering the permeation of gas molecules possessing the larger molecular size, while CNTs-filled MMM achieved better permeation due to their favorable intrinsic structural characteristics. The overall performance of the aligned hybrid membranes was found to be significant in contrary to single filler-based membrane systems (PSf/CNTs and PSf/rGO).

Trends and Applications in Advanced Polymeric Materials

In recent years, polymer nanocomposites and coatings have caught the attention of the research world due to their versatile properties and widespread applications. The availability of new nanoscale fillers and additives provide polymer scientists with materials and a lot of options to modify the properties of the polymeric matrix and hence widen the ambit of their applications. Increasing usage of polymer nanocomposites and their exploration for more potential applications lead to game-changing solutions to many engineering and technological problems. The issue with nanoscale fillers is their stability and compatibility with polymeric matrix. A lot depends on the processing protocols used for fabricating the nanocomposites. This chapter provides an overview of the structure-propertyprocessing relationship for polymer nanocomposites and coatings.