LAYER-BY-LAYER DIRECTLY-ASSEMBLY OF POLYELECTROLYTE MULTILAYERS WITH FOAMING STRUCTURES A Thesis Presented to The Graduate Faculty of The University of Akron In Partial Fulfillment of the Requirements for the Degree Master of Science Lihua Xu August, 2015 LAYER-BY-LAYER DIRECTLY-ASSEMBLY OF POLYELECTROLYTE MULTILAYERS WITH FOAMING STRUCTURES Lihua Xu Thesis Approved: Accepted: _____________________ _____________________ Advisor Department Chair Dr. Nicole Zacharia Dr. Sadhan C. Jana _____________________ _____________________ Co-Advisor Dean of the College Dr. Kevin Cavicchi Dr. Eric J. Amis _____________________ _____________________ Committee Member Interim Dean of the Graduate School Dr. Sadhan C. Jana Dr. Rex D. Ramsier _____________________ _____________________ Committee Member Date Dr. Mark D. Soucek ii ABSTRACT In recent decades, dynamic Layer-by-Layer (LbL) assembly of multilayer thin films has been widely recognized for many reasons, especially for its versatile functionality and ease of fabrication.1-3 Films can be fabricated towards huge amounts of materials, such as polyelectrolytes, organic components, polymeric microgels, etc. 4-7 Through the long history of LbL assembly research, few papers proposed ideas of making porous films or foamed films directly or indirectly, as foamed material contained plenty of pores, which could be used in insulation materials and fast food-packages.8-9 In several papers, the step of acid treatment aimed for irreversible structure transformation applied into films fabricated by the LbL assembly method.10 This indirect method makes procedures more complex, so direct fabrication with LbL is necessary. However, time- consuming problems and challenges from external environmental factors still limits the development of this technique. In this thesis, a facile fabrication of porous films through the LbL assembly method was introduced. Strong polyelectrolyte, polycation poly(diallyldimethylammoniu -m chloride) (PolyDADMAC) and polyanion poly(styrene sulfonate acid) (PSSA) are utilized as the original material. And PolyDADMAC was slightly modified by sodium hydroxide (NaOH) and carbon dioxide (CO2) in order to get the bicarbonate structure at the side groups along the chain of the polyelectrolyte. In order to deeply study the films, some other particles, such as the surfactant brij-76 and RDS laponite were added into certain solutions for comparison. iii Films were achieved by alternately putting clean glass slides into the polycation and polyanion solutions with the rinsing step in between. 20-bilayer film can be achieved after repeating the procedures above 20 times. The principle is that the bicarbonate functional group will react with the hydrogen ions for the sake of letting the gas carbon dioxide out and then make the porous structure throughout the film. The morphology of the films measured by an atomic force microscope (AFM) and a scanning electron microscope (SEM) shows that porous structures are obvious through the whole film when no sodium bicarbonate (NaHCO3) is added into the anion solution. The results help to solve the problem of directly making the foaming films as well as simplifying the procedures. iv ACKNOWLEDGEMENTS I would like to express my great appreciations to my advisors Prof. Nicole S. Zacharia and Prof. Kevin A. Cavicchi for their invaluable suggestions and guidance, both in scientific research and in my daily life. Thanks to their encouragement and support, I became confident in myself and eventually finished this Master's thesis. Also I would like to thank all my committee members. In addition, I appreciate the collaboration and advice from group members. Especially for Mr. Guodong Deng who helped me a lot on the measurements of using an Atomic Force Microscope (AFM). Finally, I would like to express my gratitude towards my beloved parents and sister for their patience as well as their financial support to make this thesis complete. v TABLE OF CONTENTS Page LIST OF TABLES ..........................................................................................................viii LIST OF FIGURES............................................................................................................ix CHAPTER...........................................................................................................................1 I. INTRODUCTION............................................................................................................1 1.1 Layer-by-Layer(LbL) assembly.....................................................................................1 1.1.1 Basic concepts about LbL assembly.......................................................................1 1.1.1.1 History of development of LbL assembly........................................................1 1.1.1.2 Research fields using LbL assembly technique................................................2 1.1.1.3 Materials used for LbL assembly......................................................................3 1.1.1.4 Factors influence films made by LbL assembly...............................................3 1.1.1.5 The interactions existing in the LbL film.........................................................4 1.1.2 Substrates for constructing LbL film.....................................................................4 1.1.3 Methods operated in the LbL assembly..................................................................6 1.1.3.1 Dipping LbL assembly......................................................................................8 1.1.3.2 Spin-assisted LbL assembly..............................................................................9 1.1.3.3 Spray-assisted LbL assembly..........................................................................12 1.1.3.4 Other film-making methods............................................................................14 1.2 Polyelectrolyte.............................................................................................................17 1.2.1 Basic concepts about polyelectrolyte.................................................................17 1.2.2 Commonly used polyelectrolytes.......................................................................19 II. MOTIVATION AND PROBLEM STATEMENT.......................................................21 2.1 Motivation....................................................................................................................21 2.2 Problem statement.......................................................................................................25 III. EXPERIMENT SECTIONS........................................................................................26 vi 3.1 Material........................................................................................................................26 3.2 Treatment of the substrates..........................................................................................28 3.3 Solution preparation.....................................................................................................28 3.4 Layer-by-Layer assembly............................................................................................31 3.5 Machine used in the experiment and the sample preparations....................................33 IV. RESULTS AND DICUSSIONS..................................................................................36 4.1 Compare the structure of the different films................................................................36 4.2 Analyzing SEM images of these different films..........................................................38 4.3 AFM images of 1-6 bilayers of 4 typical films............................................................44 4.4 Thickness and roughness measurements.....................................................................50 4.5 TGA data illustrates the content of the film.................................................................52 V. CONCLUSION.............................................................................................................54 REFERENCES..................................................................................................................55 vii LIST OF TABLES Table Page 1. The components of different solutions to make different films.....................................33 viii LIST OF FIGURES Figure Page 1. Classification of substrates used in fabrication of layer-by-layer self-assembly. Copyright 2014 Nano-biomedicine.45..................................................................................5 2. Schematic representation of the processes used to fabricate polyelectrolyte multilayer films by LbL assembly. (a) Dip coating: glass slides and beakers are used in this method. Steps 1) and 3) represent the exposure of a polyanion and polycation respectively, and steps 2) and 4) are rinsing steps. The four steps are in the basic build-up sequence and contribute for only one-bilayer film architecture. If 10-bilayer film is needed, the four procedures would be repeated 10 times. Construction of more complex film requires additional beakers and an extended deposition sequence. (b) Spin-assisted LbL assembly: High spinning speed would be operated after the droplet of the material is applied onto the center of the substrate surface. And the rinsing step would take place between steps 1) and 3), all the four steps are in a circulation system. (c) Spray-assisted LbL assembly: Instead of bringing the substrates surface into