Reconfigurable Polymer Interfaces for Dynamic Interactions and Differentiation of Soft Colloids

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PART 1: NON-TECHNICAL SUMMARY Phenomena derived from the exposure of surfaces of polymeric materials to their environment or in contact with other materials are relevant to many practical applications. Dynamically changing polymer interfaces are an important class of materials that adapt their properties upon external stimuli according to a preprogrammed scenario. This project aims for the development and study of specially designed polymer interfaces which, in response to stimuli, could attract and repel microscopic objects such as colloids, liquid droplets, particles, vesicles, viruses, or biological cells. Dynamic switching between repulsion and attraction will be adjusted and used for selection, differentiation, and isolation of the particulates. Such dynamic interfaces could be able to extract and remove traces of particles of toxic and hazardous materials, soil particles, oil droplets, bacteria, and viruses from various media such as drinking water, blood, food, and surfaces of commodity and specialty materials and devices. On the other side, such dynamic interfaces would be able to differentiate and extract valuable particulates if they are very diluted in mixtures with other ingredients, for example sediments containing noble and rare metals, some types of human stem cells and other biological samples, and samples of soils in agricultural fields and in space missions. The major challenge being addressed in the project is to understand the complex dynamic mechanisms of the interaction of functional polymer interfaces with various particulates possessing different properties and then to apply the obtained knowledge for proper design of the reconfigurable dynamic interfaces. This project also provides a mechanism to educate a new generation of professionals capable of creative and transformative thinking. Advanced polymer science research is attracting many talented young men and women of different backgrounds and training levels, including high school, undergraduate, graduate students and postdoctoral scholars, who care and feel responsible for the development of a strong and healthy national economy, clean and sustainable environment, and societal prosperity. This project will serve the purpose of developing their skills and experience.PART 2: TECHNICAL SUMMARYInteractions with polymer interfaces via adsorption-desorption mechanisms are limited by the quasi-irreversible adsorption character of polymers, i.e., approaching the equilibrium is hampered by very slow desorption kinetics due to a high activation free energy of the detachment of all adsorbed segments at once. These properties are revealed as strong and quasi-irreversible adsorption of colloidal particulates, liquid droplets, vesicles, proteins, microbes, etc. on the surface of various materials. Whereas this inherent property of polymeric interfaces is advantageous for adhesive applications, this adhesion hysteresis causes complications for affinity-based discrimination of various particulates in complex mixtures for numerous applications. This project aims to develop a novel mechanism of surface differentiation and selective transport of soft colloids owing to dynamic polymeric surfaces with specially designed functionality, microstructure, and dynamic response. This mechanism will be realized by exploring dynamically oscillating polymer interfaces made of distinctive attractive, adhesive, and repulsive micro-domains of microstructured polymer brushes that undergo temperature-driven phase transitions. The adhesive domains will have covalently bound functional motifs that target complementary motifs on the surface of soft colloids of interest. The 2D-interfaces will be designed with anisotropic patterns of microdomains. The different microdomains will have variable dimensions and surface concentration of the specific motifs. A traveling temperature gradient will be applied to facilitate directed transport of soft colloids. The key challenges of the study consist in developing a fundamental understanding of the dynamic interaction of the microstructured polymer-brush interfaces with the soft colloids having different dimensions, elasticity, and composition of surface functional groups, as well as relaxation times. The attachment-detachment dynamic equilibrium controlled by osmotic pressure of swollen repulsive domains, deformation of soft particles, entropic penalty of stretched adhesive domains, and adhesion energy of complimentary motifs will be analyzed in specially designed experiments using soft lipid or block-copolymer vesicles and compared with results of computer simulations. .This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.