Publications by authors named "Samuel A Pendergraph"

8 Publications

  • Page 1 of 1

Strong and tuneable wet adhesion with rationally designed layer-by-layer assembled triblock copolymer films.

Nanoscale 2016 Oct;8(42):18204-18211

KTH Royal Institute of Technology, School of Chemical Science and Engineering, Department of Fibre and Polymer Technology, Teknikringen 56, SE-100 44 Stockholm, Sweden. and KTH Royal Institute of Technology, Wallenberg Wood Science Centre, Teknikringen 56, SE-110 44 Stockholm, Sweden.

In this study the wet adhesion between Layer-by-Layer (LbL) assembled films of triblock copolymer micelles was investigated. Through the LbL assembly of triblock copolymer micelles with hydrophobic, low glass transition temperature (T) middle blocks and ionic outer blocks, a network of energy dissipating polymer chains with electrostatic interactions serving as crosslinks can be built. Four triblock copolymers were synthesized through Atom Transfer Radical Polymerisation (ATRP). One pair had a poly(2-ethyl-hexyl methacrylate) middle block with cationic or anionic outer blocks. The other pair contained the same ionic outer blocks but poly(n-butyl methacrylate) as the middle block. The wet adhesion was evaluated with colloidal probe AFM. To our knowledge, wet adhesion of the magnitude measured in this study has not previously been measured on any polymer system with this technique. We are convinced that this type of block copolymer system grants the ability to control the geometry and adhesive strength in a number of nano- and macroscale applications.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1039/c6nr05659hDOI Listing
October 2016

Nanometer smooth, macroscopic spherical cellulose probes for contact adhesion measurements.

ACS Appl Mater Interfaces 2014 Dec 20;6(23):20928-35. Epub 2014 Nov 20.

KTH Royal Institute of Technology , School of Chemical Science and Engineering, Department of Fibre and Polymer Technology, SE-100 44 Stockholm, Sweden.

Cellulose spheres were prepared by dissolving cellulose fibers and subsequently solidifying the solution in a nonsolvent. Three different solution concentrations were tested and several nonsolvents were evaluated for their effect on the formation of spheres. Conditions were highlighted to create cellulose spheres with a diameter of ∼1 mm and a root-mean-square surface roughness of ∼1 nm. These solid spheres were shown to be easily chemically modified without changing the mechanical properties significantly. Contact adhesion measurements were then implemented with these spheres against a poly(dimethylsiloxane) (PDMS) elastomer in order to quantify the adhesion. Using Johnson-Kendall-Roberts (JKR) theory, we quantified the adhesion for unmodified cellulose and hydrophobic cellulose spheres. We highlight the ability of these spheres to report more accurate adhesion information, compared to spin-coated thin films. The application of these new cellulose probes also opens up new possibilities for direct, accurate measurement of adhesion between cellulose and other materials instead of using uncertain surface energy determinations to calculate the theoretical work of adhesion between cellulose and different solid materials.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/am505673uDOI Listing
December 2014

Robust and tailored wet adhesion in biopolymer thin films.

Biomacromolecules 2014 Dec 6;15(12):4420-8. Epub 2014 Nov 6.

KTH Royal Institute of Technology , †Fibre and Polymer Technology and ‡Wallenberg Wood Science Centre, Teknikringen 56, SE-100 44 Stockholm, Sweden.

Model layer-by-layer (LbL) assemblies of poly(allylamine hydrochloride) (PAH) and hyaluronic acid (HA) were fabricated in order to study their wet adhesive behavior. The film characteristics were investigated to understand the inherent structures during the assembly process. Subsequently, the adhesion of these systems was evaluated to understand the correlation between the structure of the film and the energy required to separate these LbL assemblies. We describe how the conditions of the LbL fabrication can be utilized to control the adhesion between films. The characteristics of the film formation are examined in the absence and presence of salt during the film formation. The dependence on contact time and LbL film thickness on the critical pull-off force and work of adhesion are discussed. Specifically, by introducing sodium chloride (NaCl) in the assembly process, the pull-off forces can be increased by a factor of 10 and the work of adhesion by 2 orders of magnitude. Adjusting both the contact time and the film thickness enables control of the adhesive properties within these limits. Based on these results, we discuss how the fabrication procedure can create tailored adhesive interfaces with properties surpassing analogous systems found in nature.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/bm501202sDOI Listing
December 2014

Enhancing adhesion of elastomeric composites through facile patterning of surface discontinuities.

ACS Appl Mater Interfaces 2014 May 25;6(9):6845-50. Epub 2014 Apr 25.

Department of Polymer Science and Engineering, University of Massachusetts , 120 Governors Drive, Amherst, Massachusetts 01003-9265, United States.

Patterning interfaces can provide enhanced adhesion over a projected area. However, careful consideration of the material properties and geometry must be applied to provide successful reversible adhesives. We present a simple method to use patterned, elastomeric fabric composites to enhance the shear adhesion strength by nearly 40% compared to a non-patterned sample. We describe how this enhancement depends on the pattern geometry, the velocity dependence of the adhesive materials, and the controlled displacement rate applied to the interface. Through these observations, we discuss strategies for improving reversible adhesives.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/am5006546DOI Listing
May 2014

Facile colloidal lithography on rough and non-planar surfaces for asymmetric patterning.

Small 2013 Sep 28;9(18):3037-42. Epub 2013 Feb 28.

Department of Polymer Science and Engineering, University of Massachusetts Amherst, 120 Governors Drive, Amherst, MA 01003-9263, USA.

Free-standing colloidal arrays can be easily transferred to supported fibers. These films conform and provide the template to have consistent submicrometer and nanometer features transferred to the periphery of rough, 7 μm diameter fibers. This technique is adjustable to a number of fiber surfaces and colloidal template sizes.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1002/smll.201202821DOI Listing
September 2013

Opportunities with fabric composites as unique flexible substrates.

ACS Appl Mater Interfaces 2012 Dec 21;4(12):6640-5. Epub 2012 Nov 21.

Department of Polymer Science and Engineering, University of Massachusetts, 120 Governors Dr. Amherst, Massachusetts 01003-9265, USA.

Flexible substrates enable new capabilities in applications ranging from electronics to biomedical devices. To provide a new platform for these applications, we investigate a composite material consisting of rigid fiber fabrics impregnated with soft elastomers, offering the ability to create load bearing, yet flexible substrates. We demonstrate an integrated and facile one-step imprint lithographic patterning method on a number of fabrics and resins. Furthermore, the bending and tensile properties were examined to compare the composites to other flexible materials such as PET and cellulose paper. Carbon fiber composites possess a higher tensile modulus than PET while retaining almost an order of magnitude lower bending modulus. Fabric composites can also have anisotropic mechanical properties not observed in homogeneous materials. Finally, we provide a discussion of these anisotropic mechanical responses and their potential use in flexible applications.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/am3017812DOI Listing
December 2012

Conjugated Polymers Atypically Prepared in Water.

J Polym Sci A Polym Chem 2010 May;48(9):2024-2031

Department of Chemistry and the Polymer Program, Institute of Materials Science, University of Connecticut, 97 N. Eagleville Rd., Storrs, CT 06269.

Processability remains a fundamental issue for the implementation of conducting polymer technology. A simple synthetic route towards processable precursors to conducting polymers (main chain and side chain) was developed using commercially available materials. These soluble precursor systems were converted to conjugated polymers electrochemically in aqueous media, offering a cheaper and greener method of processing. Oxidative conversion in aqueous and organic media each produced equivalent electrochromics. The precursor method enhances the yield of the electrochromic polymer obtained over that of electrodeposition, and it relies on a less corruptible electrolyte bath. However, electrochemical conversion of the precursor polymers often relies on organic salts and solvents. The ability to achieve oxidative conversion in brine offers a less costly and a more environmentally friendly processing step. It is also beneficial for biological applications. The electrochromics obtained herein were evaluated for electronic, spectral, and morphological properties.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1002/pola.23972DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2955856PMC
May 2010

Gold nanoparticles with externally controlled, reversible shifts of local surface plasmon resonance bands.

Langmuir 2009 Nov;25(22):13120-4

Department of Chemistry, University of Connecticut, Storrs, Connecticut 06269, USA.

We have achieved reversible tunability of local surface plasmon resonance in conjugated polymer functionalized gold nanoparticles. This property was facilitated by the preparation of 3,4-ethylenedioxythiophene (EDOT) containing polynorbornene brushes on gold nanoparticles via surface-initiated ring-opening metathesis polymerization. Reversible tuning of the surface plasmon band was achieved by electrochemically switching the EDOT polymer between its reduced and oxidized states.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/la901779kDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2911025PMC
November 2009