Nanoscale Characterization of Nanostructured Polymer Films and

Chapter 15

Nanoscale Characterization of Nanostructured Polymer Films and Coatings 1

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Louis T. Germinario , Emmett P. O'Brien , John W. Gilmer , and Shriram Bagrodia Downloaded by DUKE UNIV on January 18, 2013 | http://pubs.acs.org Publication Date: June 12, 2009 | doi: 10.1021/bk-2009-1008.ch015

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1Eastman Chemical Company, Lincoln Street, B-150B, Kingsport, TN 37662-5150 King College, 1350 King College Road, Bristol, TN 37620 C E R E P L A S T , Inc., 3411-3421 West E l Segundo Boulevard, Hawthorne, C A 90250 2

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The manipulation of matter on the nanometer scale has led to the development and commercialization of polymeric materials in which individual molecules are integrated into larger structural hierarchies in part by self organization of building blocks.(1) Continued development of such structures and the ability to control their morphology at the molecular level requires the use of a multidisciplinary approach for materials characterization for establishing structure-property -relation-ships. Advanced characterization methods and protocols developed for analysis of surfaces and interfaces will be reviewed with an emphasis on examples drawn from industrial problem-solving. Examples include different classes of polymeric materials that employ either silica colloids, surfactants or homopolymers and copolymers of polyesters, polycarbonates, polyolefins, epoxies or acrylates. These materials as a result of new structuring achieve improved performance characteristics such as adhesion, hardness, scuff and scratch resistance and barrier properties.

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© 2009 American Chemical Society

In Nanotechnology Applications in Coatings; Fernando, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2009.

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Downloaded by DUKE UNIV on January 18, 2013 | http://pubs.acs.org Publication Date: June 12, 2009 | doi: 10.1021/bk-2009-1008.ch015

Introduction The analytical problem posed by characterization of nanostructured materials include, spatial localization of points and regions of interest (resolution), elemental and molecular identification of components (detectability), and determination of the concentration of detected molecular species (sensitivity). Analytical techniques found to be most suitable for characterization of nanostructured materials include atomic force microscopy (AFM), nanoindentation, Nano-Thermal analysis, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Other analytical tools such as Infrared spectroscopy and dynamic mechanical analysis (DMA) were also employed for identification of organic moieties and measurement of viscoelastic and rheological properties. Molecular modeling tools were also used to generate low energy molecular 3D structures that were optimized in MOPAC using PM3 parameters. MOPAC (Molecular Orbital PACkage) is a popular computer program designed to implement semi-empirical quantum chemistry algorithms, such as PM3 (Parameterized Model number 3). As a result, PM3 provides a semi-empirical method for the quantum calculation of molecular electronic structures. Computed structures were used to compare structures and geometries measured experimentally by A F M .

Molecular Self-assembly and Ordering of Alkyl-polyglycosides for Improved Adhesion in Paper Coatings Cellulose is the most abundant polymer found in nature and in some forms is used as heat sealable paper for medical packaging where it acts as a filter to particulates and microorganisms while at the same time permitting free passage of gas and water vapor during sterilization. This paper must also be heat sealable over plastic trays that contain medical instrumentation. The bond of the paper to the plastic must also be sufficiently strong, but at the same time, pealable from the plastic tray as needed. The additive that was found to be suitable as an adhesion promoter was alkylpolyglycoside (APG) which also has commercial utility as a nonionic surfactant (Figure 1).(2) APG as a paper additive has been used as a softener for tissue paper.(3) As a coating for paper, APG has been used in combination with petroleum wax as a barrier coating.(4) For heat sealable paper, the initial hypothesis was, upon application of APG to Cellulose Acetate (CA) containing paper, APG would anchor itself in the cellulosic matrix, act as a plasticizer for CA, and present a hydrophobic surface to one side of the paper.(5) In order to define the role and possible interactions of APG within the paper structure, A F M was used as a principal tool to localize APG on APG-treated paper surfaces. A F M has been widely used for the direct imaging of Langmuir-



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Figure 1. AFM ofpaper containing 25% cellulose acetate, coated with a 3% solution ofAPG (DP = 1.5, R= average alkyl chain length = 9.9). (A) is the height image, while (B) is a phase image. A drawing is also shown of the cellulose structure and the corresponding structure ofAPG and an R-group corresponding to a 10 residue alkyl chain.

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296 Blodgett (LB) films, without the need for making replicas.(6) Characterization of self-assembly and structuring of APG on paper fiber surfaces proved to be somewhat challenging. In this account, paper containing 25% cellulose acetate was coated with a 3% solution of APG, (degree of polymerization (DP = 1.5, R= average alkyl chain length = 9.9). Large cellulose fibers are seen to traverse across the field of view (Figure 1A and IB). Figure 1A is a height image which provides topographic information while Figure IB is a phase image whose contrast correlates with viscoelasticity. The molecular drawing is a structure of cellulose and APG with an R-group corresponding to a 10 residue alkyl chain. The surface of this coated paper and the corresponding uncoated paper was further examined by AFM. Figure 2 provides a top-view of a coated cellulose fiber. In the left image (Figure 2A), the bright patches correspond to high points on the fiber surface while the dark regions are valleys. The corresponding right image (Figure 2B) is a phase image of the same fiber area in which the darker regions are indicative of soft domains, while the lighter areas are representative of hard domains. Three-dimensional views of fiber surfaces from coated versus uncoated paper (Figure 3) show the presence of surface patches that are not present in the corresponding areas of uncoated paper. Collectively, this data is interpreted as indicating that the soft patches correspond to APG-rich areas. AFM-based bearing analysis was used to obtain information on the molecular dimensions of APG by measuring the thickness of the coating from height data (Figure 3). Bearing analysis generates a histogram of surface feature heights and provides a method for analyzing and plotting the distribution of surface heights. The boxed regions drawn in images in Figure 3 were taken from two different fiber areas. As can be seen, bearing analysis from these regions depict surface features with average heights of 3.6 nm, while uncoated fibers display an average surface height of

Nanoscale Characterization of Nanostructured Polymer Films and

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