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Preface This book results from the symposium “Surfactants and Amphiphilic Polymers: Fundamentals and Applications” held at the 239th ACS National Meeting in San Francisco, CA on March 21-25, 2010. The symposium was sponsored by the ACS Division of Colloid and Surface Chemistry as part of its continuing symposia series on surfactants and association colloids. Approximately 70 papers were presented at this symposium and the book chapters represent a sampling of problems addressed. Amphiphilic molecules, whether they are low molecular weight conventional surfactants or high molecular weight amphiphilic polymers, display characteristic molecular self-assembly behavior in solutions, at interfaces and in bulk, generating nanoscale structures. These nanoscopic assemblies are being widely exploited for applications in materials, energy, pharmaceutical and biomedical technologies. There is great interest in the design of novel amphiphilic systems that will give rise to interesting structural morphologies following molecular assembly. This would allow the amphiphilic systems to be tailored for specific applications. Successful development of such amphiphilic systems requires (i) methods to synthesize novel amphiphilic molecules, (ii) understanding the molecular assembly behavior in a variety of environments as a function of the chemical structure of the amphiphiles, and (iii) finding ways to utilize the molecular assemblies in a robust way in practical applications. The proposed book addresses these essential themes in the study of amphiphilic systems. The papers incorporated in the book cover a wide variety of amphiphiles including low molecular weight surfactants with novel ionic head groups, surfactants with chirality, peptoid amphiphiles, block copolymers, and block polyelectrolytes. In addition, other self assembling systems such as self-assembled monolayers of small molecules and polymer brushes are considered. Each of the papers includes one or more of the following aspects: synthesis of amphiphiles with novel chemical features, characterizing the assembly of amphiphiles in solutions, bulk or at interfaces, application of the amphiphilic system, or modeling the assembly behavior of the amphiphilic system. The book starts with comparative molecular scale theories of self-assembly of low molecular weight surfactants and amphiphilic block copolymers. In this first Chapter, it is shown that analogous formulations of free energy models for aggregation coupled to molecular packing considerations can predict the self-assembly behavior for both classes of amphiphiles. Changes in the morphology of aggregates resulting from variations in the chemical structures of the amphiphile or in the solution conditions are satisfactorily predicted by the phenomenological theory. ix In Amphiphiles: Molecular Assembly and Applications; Nagarajan, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 2011.
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The molecular structural features of amphiphiles and their impact on self-assembly and/or potential applications are considered in many chapters. Ilies and coworkers have presented a comprehensive discussion of design of amphiphiles with pyridinium polar head for nucleic acid delivery in Chapter 2. The impact of various structural characteristics of the amphiphile (hydrophobic chain type, linkage type, counterion) on the transfection activity and cytotoxicity is discussed for various classes of pyridinium amphiphiles (detergents, lipids, gemini surfactants, lipophilic polycations). In Chapter 3, Robinson et al discuss their synthesis of a family of novel amphiphile, helical peptoids, with structural motifs similar to the m13 bacteriophage. They show that is possible to tune the interaction of peptoids with double-stranded DNA through variation of the side group sequence, thereby suggesting a potential use of such peptoids in gene delivery and structural DNA applications. Carbohydrate surfactants based on uronic acid are described in Chapter 4. In this chapter, experimental measurements of both dynamic and equilibrium properties at air-liquid and liquid-liquid interfaces for the uronic amphiphiles relevant to their use in emulsions and foams are reported. Lo Nostro et al, discuss the self-assembly and interfacial properties of amphiphiles with chiral head groups, L-ascorbyl-alkanoates (L-ASC) and D-isoascorbyl-alkanoates (D-ASC), in Chapter 5, in terms of the differing stereochemistries of the surfactant head groups that determine the inter- or intramolecular interactions. Using differential scanning calorimetry, infrared spectra, and X-ray diffraction experiments in the solid and in the coagel states, they reveal chirality dependent phase behavior for mixtures of L-ASC12 and D-ASC12. In Chapter 6, Klapper et al show that oil-in-oil type of emulsions can be effectively stabilized by amphiphilic polymers. Using polystyrene-b-polypentafluro styrene and polyisoprene-b-polymethyl methacrylate, they formulated stable emulsions of n-hexane / DMF and toluene / perfluoro methyl cyclohexane which were then used as aprotic reaction media for emulsion polymerization applications. The molecular assembly between fluorinated polyelectrolytes such as perfluoro sulfonic acid PTFE copolymer (i.e. Nafion®) and poly(vinyl alcohol) (PVA) or poly(allyl amine) (PAH) is shown to involve fluorinated hydrogen bonds by Farhat. In this chapter, the formation of hydrogels from these systems is described and it is shown that these hydrogels can effectively replace liquid electrolyte solutions for the purpose of making miniature solid-state electrochemical systems. Novel characterization methods have been employed to look at the structural and morphological properties of self-assembled nanostructures. Electrokinetic sonic amplitude technique has been used by Eisenbach and coworkers to determine the nature of adsorbed layers of amphiphilic polymers on hydrophilic titanium dioxide and hydrophobic copper phthalocyanine surfaces, in Chapter 8. The contrasting impact of the surface-polymer interactions on the morphology of the polymer adsorbed layer is discussed. Atomic force microscopy and neutron reflectivity measurements are used by Takahar et al in Chapter 9 to study the thickness of polymer brush under different salt conditions. Existence of attractive electrostatic interactions at low salt concentrations and their screening at high salt concentrations are shown to dramatically change the structure and dimensions of the polymer at the interface. The application of quartz crystal microbalance with x In Amphiphiles: Molecular Assembly and Applications; Nagarajan, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 2011.
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dissipation monitoring (QCM-D) for determining the viscoelastic properties of soft materials, such as vesicles and microemulsions near surfaces is reviewed by Lane in Chapter 10. Knock and Sanii use QCM-D as a mass sensing device to examine the adsorption of single and double chain ionic surfactants on hydrophilic and hydrophobic surfaces in Chapter 11. Atomic force microscopy, contact angle goniometry and Diffuse Reflectance Infrared Fourier Transform Spectroscopy were used to study the stability of molecular films assembled on steel surfaces In Chapter 12. Here, Lim et al assembled a molecular layer of amphiphilic alkyl phosphonic acid on the steel surface and thermally reacted to create a surface resistant to biofouling for application in medical devices. A new class of amphiphiles termed amphiphilic inverted polymers with hydrophobic and hydrophilic moieties, alternately distributed along the main polymer backbone are described in Chapter 13. Here, Voronov and coworkers report the micelle formation properties of these polymers including critical micelle concentration, micelle size and solubilization and also their ability to invert their morphologies when the solvent polarity is modified. Biesalski et al have synthesized a new class of amphiphiles by modifying di-acetylenic fatty acids at the carboxylic acid head-group with either cell-adhesive or mussel-adhesive peptide sequences. In Chapter 14, they show that the resulting amphiphiles can be stabilized by UV-light induced polymerization of the hydrophobic tail into well-defined structures that allow the presentation of the adhesive groups at the vesicular surface. Applications of self-assmbled amphihliar structures to material synthesis are discussed in many chapters. Mandal and Kruk manipulate block copolymer liquid crystal structures by controlling the amount of hydrocarbon solubilized and have used them as templates to produce large-pore organosilicas. In Chapter 15 they describe the preparation of organosilica materials with nominal pore sizes of 18 and 10 nm employing a synthesis procedure carried out at room temperature. In contrast, a template free synthesis of nanocapsules by polymerization of the macrocyclic compound, resorcinarenes, is described by Balasubramanian and Kalaitzis in Chapter 16. The photopolymerization is found to yield nanostructures of different morphologies besides nanocapsules, depending on the choice of the solvent. In Chapter 17, the preparation of polymer capsules with oil cores is reported by Adalsteinsson et al using a kinetically stable, miniemulsion as the template The book also includes theoretical and computer simulation studies of new problems in amphiphile self-assembly. Molecular dynamic simulations in combination with statistical mechanics have been applied by Nielsen group to predict assembly of nanoparticles and surfactants at the oil-water interface for systems consisting only of nanoparticles, competing or cooperating mixtures of nanoparticles and nonionic surfactants and for nanoparticles chemically functionalized with surfactants on their surfaces in Chapter 18. The simulation results for molecular organization behavior as well as for the reduction of oil-water interfacial tensions are presented. The contributing authors for thus book come from a wide cross-section of US universities and national laboratories and a third of the contributors are from xi In Amphiphiles: Molecular Assembly and Applications; Nagarajan, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 2011.
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abroad. The affiliations of the authors are representative of the broad theoretical and practical interest in amphiphile systems and their applications. The editor is thankful to the numerous reviewers. The reviewers of individual chapters contributed prompt critical reviews that have helped improve the quality of the manuscripts. The Editor acknowledges support from ACS Books, especially Tim Marney, with the use of the newly introduced on-line manuscript submissions process. The Editor acknowledges the support from Natick Soldier Research, Development & Engineering Center, that allowed him to organize the symposium and develop this book based on selected contributions.
R. Nagarajan
Molecular Sciences and Engineering Team Natick Soldier Research, Development & Engineering Center Natick, MA
xii In Amphiphiles: Molecular Assembly and Applications; Nagarajan, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 2011.
