Investigation of Cellulose Nitrate Motion Picture Film Chemical Decomposition & Associated Fire Risk

This grant will support empirical research about the related threats of cellulose nitrate motion picture decay and flammability. The project will be co-investigated by two University of Wisconsin-Madison institutions--the Wisconsin Center for Film & Theater Research and the Mahanthappa Research Group--in partnership with the Wisconsin Historical Society. Used as the base for all professionally-produced motion pictures made between the 1890s and the early 1950s, cellulose nitrate is chemically unstable and highly flammable. Unfortunately, very little data about these risks is available to the preservation community. Project results will be published in a white paper targeted at an audience of archival professionals, and, as relevant, in amendments to the International Standard (ISO) and National Fire Protection Association (NFPA) standards on nitrate handling and storage

Characteristics of Lamellar Mesophases in Strongly Segregated Broad Dispersity ABA Triblock Copolymers

We report the synthesis and characterization of a series of 13 strongly segregated poly­(lactide-<i>b</i>-1,4-butadiene-<i>b</i>-lactide) (LBL) triblock copolymers, in which a broad dispersity center B segment (<i><i><i>Đ</i></i></i> = <i>M</i>_w/<i>M</i>_n ∼ 1.7–1.9) is embedded between two narrow dispersity L end blocks (<i><i><i>Đ</i></i></i> ≤ 1.20). Derived from chain transfer ring-opening metathesis polymerization (ROMP-CT) of 1,5,9-cyclododecatriene in the presence of 1,4-diacetoxy-2-butene, α,ω-dihydroxytelechelic poly­(1,4-butadienes) serve as ring-opening transesterification polymerization (ROTEP) macroinitiators for the parallel synthesis of LBL triblock copolymers with <i>M</i>_n = 12.4–28.7 kg/mol and volume fractions <i>f</i>_B = 0.44–0.79. By determining the Flory–Huggins interaction parameter χ_LB = 0.192 at 155 °C from mean-field theory analyses of synchrotron X-ray scattering profiles for a narrow dispersity LB diblock copolymer, we estimate that the segregation strengths associated with the broad dispersity LBL copolymers range χ_LB<i>N</i> = 35.1–83.6. As compared to their narrow dispersity analogues reported herein, broad B segment dispersity shifts the composition-dependent lamellar phase window in LBL triblocks to higher values of <i>f</i>_B = 0.52–0.75. Contrary to previous reports of substantial dispersity-induced, lamellar domain spacing dilation in weakly segregated AB diblock and ABA triblock copolymers, strongly segregated LBL copolymers exhibit surprisingly similar domain sizes and scaling relations (<i>d</i> ∝ <i>N</i>^0.72±0.06) to their narrow dispersity analogues. This finding suggests that the magnitude of χ_AB determines the moment of the molar mass distribution that controls the observed lamellar domain spacing

Synthesis and Rheological Characterization of Poly(vinyl acetate‑<i>b</i>‑vinyl alcohol‑<i>b</i>‑vinyl acetate) Triblock Copolymer Hydrogels

We report the synthesis and shear rheology of a series of hydrogels derived from poly­(vinyl acetate-<i>b</i>-vinyl alcohol-<i>b</i>-vinyl acetate) (PVAc-<i>b</i>-PVOH-<i>b</i>-PVAc) triblock copolymers. Bidirectional, reversible-addition–fragmentation chain transfer free radical polymerizations of vinyl acetate (VAc) and vinyl chloroacetate (VClAc) are optimized to produce a series of relatively narrow dispersity PVAc-<i>b</i>-P­(VAc-<i>ran</i>-VClAc)-<i>b</i>-PVAc triblock copolymers with controlled molecular weights and compositions. Rapid and selective hydrolysis of P­(VAc-<i>ran</i>-VClAc) blocks with K₂CO₃/CH₃OH furnishes access to a series of PVAc-<i>b</i>-PVOH-<i>b</i>-PVAc amphiphiles. Hydration of solvent-cast films of these copolymers, comprising PVAc blocks of comparable degrees of polymerization with variable PVOH segment lengths, yields soft hydrogels (<i>G</i>′(ω) ∼ 1–10 kPa). Synchrotron small-angle and wide-angle X-ray scattering reveals that these hydrogels microphase separate into spherical hydrophobic PVAc domains that are interconnected by solvated PVOH network strands. The strain-dependent rheology of these hydrogels depends sensitively on the length of the center PVOH segment. This gel rheology is shown to stem from the hydrogen bond donor–acceptor capabilities of PVOH, which leads to the formation of weak, dynamic noncovalent crosslinks in the aqueous domains of these gels. Thus, the observed gel rheology may be rationalized in terms of the shear-induced reorganization of these H-bonding crosslinks as a function of the applied strain

Polydispersity-Driven Block Copolymer Amphiphile Self-Assembly into Prolate-Spheroid Micelles

The aqueous self-assembly behavior of polydisperse poly­(ethylene oxide-<i>b</i>-1,4-butadiene-<i>b</i>-ethylene oxide) (OBO) macromolecular triblock amphiphiles is examined to discern the implications of continuous polydispersity in the hydrophobic block on the resulting aqueous micellar morphologies of otherwise monodisperse polymer surfactants. The chain length polydispersity and implicit composition polydispersity of these samples furnishes a distribution of preferred interfacial curvatures, resulting in dilute aqueous block copolymer dispersions exhibiting coexisting spherical and rod-like micelles with vesicles in a single sample with a O weight fraction, <i>w</i>_O, of 0.18. At higher <i>w</i>_O = 0.51–0.68, the peak in the interfacial curvature distribution shifts and we observe the formation of only American football-shaped micelles. We rationalize the formation of these anisotropically shaped aggregates based on the intrinsic distribution of preferred curvatures adopted by the polydisperse copolymer amphiphiles and on the relief of core block chain stretching by chain-length-dependent intramicellar segregation

Protonation-Driven Aqueous Lyotropic Self-Assembly of Synthetic Six-Tail Lipidoids

We report the aqueous lyotropic mesophase behaviors of protonated amine-based "lipidoids," a class of synthetic lipid-like molecules that mirrors essential structural features of the multitail bacterial amphiphile lipid A. Small-angle X-ray scattering (SAXS) studies demonstrate that the protonation of the tetra(amine) headgroups of six-tail lipidoids in aqueous HCl, HNO3, H2SO4, and H3PO4 solutions variably drives their self-assembly into lamellar (L-alpha) and inverse micellar (I-II) lyotropic liquid crystals (LLCs), depending on acid identity and concentration, amphiphile tail length, and temperature. Lipidoid assemblies formed in H2SO4(aq) exhibit rare inverse body-centered cubic (BCC) and inverse face-centered cubic (FCC) micellar morphologies, the latter of which unexpectedly coexists with zero mean curvature L-alpha phases. Complementary atomistic molecular dynamics (MD) simulations furnish detailed insights into this unusual self-assembly behavior. The unique aqueous lyotropic mesophase behaviors of ammonium lipidoids originate in their dichotomous ability to adopt both inverse conical and chain-extended molecular conformations depending on the number of counterions and their identity, which lead to coexisting supramolecular assemblies with remarkably different mean interfacial curvatures.11Nsciescopu