Topochemically polymerized sodium 10,12-pentacosadiynoate (PCDA-Na) microcrystals show an irreversible red-to-blue chromatic transition accompanied by a distinct structural evolution upon initial thermal treatment, and show a subsequent completely reversible blue-to-red chromatic transition upon further thermal stimuli. Visible absorption spectroscopy, X-ray diffraction (XRD), and differential scanning calorimetry (DSC) are used to investigate the thermochromatic transition behavior of the polydiacetylenic microcrystals. Brief quantum mechanical geometry optimization is employed to explain the lattice dimensional change during the irreversible red-to-blue chromatic transition of the metastable polydiacetylenic crystals.

Surfactant-templated mesoporous materials have attracted much attention due to their unique structures and potential applications.[1±3] Synthesis of these materials involves the formation of surfactant±inorganic nanocomposites via co-assembly of surfactant and inorganic species and subsequent surfactant removal to create mesoporous materials with controlled pore structures (e.g., hexagonal or cubic arrangement of pores or lamellar nanostructures [1,3±5] ) and with various macroscopic forms (e.g., powders, [1±3,6] particles, [7±10] thin films, [8,11±16] and fibers [17,18] ). Mesoporous thin films are of particular interest because of their potential applications as sensors, membranes, and low dielectric constant films. [13,19,20] Synthesis methods include solution deposition [12,21] and solvent evaporation-induced self-assembly (EISA). [8,13,15,16,22] In the solution deposition method, thin films spontaneously nucleate and grow from acidic aqueous silicate solutions containing high concentrations of surfactant. This slow deposition process (time scale of hours to days) usually results in hexagonally ordered granular thin films with pore channels oriented parallel to the substrate surface. The EISA route deposits thin films using a rapid dipor spin-coating process (time scale of seconds), during which solvent evaporation enriches the concentration of silicate and surfactant, inducing their co-assembly into mesostructured, defect-free surfactant±silicate thin films. [13,23] This research describes a novel approach that combines aerosol deposition [24±26] and EISA to fabricate mesostructured thin films. As shown in Figure 1, this method starts with an acidic precursor solution containing a silica source and surfactant. Solvent evaporation from the aerosol droplets enriches them in silicate and surfactant and induces their co-assembly into semi-solid mesostructured particles.[8] These semi-solid particles then further coalescence on the substrate resulting in a continuous mesostructured thin film with no evidence of its original particle morphology. Compared with the dip-coating or spin-coating processes, this method can rapidly deposit mesostructured thin films with easily controlled mesostructures on large-scale planar and non-planar substrates. Figure 1 shows the scheme of the aerosol deposition apparatus. The atomizer (TSI Model # 3076) was operated under laminar flow conditions using 2.6 L min ±1 of N 2 as the carrier/ atomization gas. The heating zone was maintained at 150 C or less. The residence times for the entrained aerosol particles in the drying and heating zones are approximately 3 s each.

tained at approximately 80 C by a heating tape and were subsequently calcined at 400 C for 4 h to remove the surfactant [16]. Mesoporous silica microparticles thus obtained were modified by surface grafting according to the procedure described by Huang and Wirth [22] adapted to N-isopropylacrylamide (NIPAAm). Hydroxyl groups were created on the silica surface by treatment with concentrated HNO 3 for 4 h and subsequent washing with ultra-pure (> 18 MX resistance) water and then drying at 110 C for 2 h under an N 2 stream. These particles (0.5 g) were then added to a reactor containing 0.5 mL of the initiator, 1-(trichlorosilyl)-2-(m/p-(chloromethyl) phenyl)ethane (Gelest), and 50 mL of anhydrous toluene. The reaction was carried out at room temperature for 12 h. The silica particles were then washed with toluene, methanol, and acetone and dried at 110 C for 2 h. Atom transfer radical polymerization (ATRP) was performed on the initiator-derivatized particles. 0.2 g of silica particles were combined with 0.107 g CuCl, 0.5 g of bipyridine, and 3 g of NIPAAm (Aldrich) in 30 mL of dimethyl formamide. The reaction flask was deoxygenated with N 2 for 40 min and then sealed under N 2 . The reaction took place at 130 C for 40 h with stirring. The grafted particles were then washed with methanol and water and dried at 70 C under a stream of N 2 .The particles were characterized by SEM (Hitachi S-800) and X-ray diffraction (Siemens D5000, Cu Ka radiation k = 1.5418 ). Particle sizes were measured from the SEM images. Surface area and pore size distribution studies were carried out using nitrogen adsorption and desorption at 77 K using a Micromeritics ASAP 2000 porosimeter. Sample preparation for cross-sectional transmission electron microscopy (JEOL 2010, 200 KV) required the particles to be embedded in an epoxy and then cross-sectioned using a Sorvall MT-5000 Ultra Microtome machine.Polymer-modified particles (1.0 mg) were added to 1.0 mL of 0.035 mM fluorescein in Tris buffer (0.05 M, pH 7.4) and were incubated at either 25 or 50 C for 2 h. The samples were then cooled down to room temperature (~25C), and equilibrated at this temperature for at least 40 min. The particles were then washed three times in fresh Tris buffer. Flow cytometry recorded the dye remaining in the particles at both 50 C and 25 C. The uptake of dye was also measured, using flow cytometry, at various temperatures to examine the temperature response of the grafted polymer.Bead suspensions were analyzed by flow cytometry using a Becton-Dickinson FACScan flow cytometer (Sunnyvale, CA) interfaced to a Power PC Macintosh using the Cell Quest software package. The FACScan is equipped with a 15 mW air-cooled argon ion laser. The laser output wavelength is fixed at 488 nm. Experimental details of these analyses have been described elsewhere [23,24].For confocal microscopy, 5.0 mg of polymer grafted particles were incubated in 0.4 mL of an aqueous solution containing 0.5 mM of rhodamine 6G (Molecular Probes) at either 25 or 50 C overnight. The samples were th...

Nanostructured porous silica particles with sizes in the micrometer to sub‐micrometer range are of great interest due to their potential applications as catalyst supports and nanocomposite materials. However, if these particles are to be used in industry, a process must be developed to affordably produce them on a large scale. This paper reports on a high‐energy ball‐milling process that has been used to create micrometer‐ to sub‐micrometer‐sized mesoporous silica particles starting from a silica xerogel prepared by a surfactant self‐assembly sol–gel process. We have studied various milling conditions such as milling media (zirconia, stainless steel, or steel‐centered nylon balls), milling time, and the presence of surfactants during milling and the resulting effect on particle size and pore structure. Results from transmission electron microscopy, scanning electron microscopy, X‐ray diffraction, light scattering, and nitrogen adsorption demonstrate the feasibility of producing large quantities of nanostructured particles by this simple milling process.