Використання лазерних діодів в рейтресінговій аберометрії

Аберометри є найбільш досконалими офтальмологічними приладами, оскільки вони дозволяють оцінювати сумарну аберацію оптичної системи ока. Однак, їх основним недоліком є висока вартість. Одним із чинників, який визначає вартість аберометра, є використання складної оптико-механічної системи керування лазерним променем, який використовують для рейтресінгу – сканування зіниці ока і сітківки

A Facile Method To Fabricate Double Gyroid as a Polymer Template for Nanohybrids

Here, we suggest a facile method to acquire double gyroid (DG) phase from the self-assembly of chiral block copolymers (BCPs*), polystyrene-<i>b</i>-poly­(l-lactide) (PS–PLLA). A wide region for the formation of DG can be found in the phase diagram of the BCPs*, suggesting that helical phase (H*) from the self-assembly of BCPs* can serve as a stepping stone for the formation of the DG due to an easy path for order–order transition from two-dimensional to three-dimensional (network) structure. Moreover, the order–order transition from metastable H* to stable DG can be expedited by blending the PS–PLLA with compatible entity. Unlike the conventional way for blending BCP with homopolymer, PS–PLLA blends are prepared by using styrene oligomer (S) to fine-tune the morphologies of the blends at which the molecular weight ratio of the S and compatible PS block (<i>r</i>) is less than 0.1. Owing to the use of the low-molecular-weight oligomer, the increase of BCP chain mobility in the blends significantly reduces the transformation time for the order–order transition from H* to DG. Consequently, by taking advantage of degradable character of the PLLA, nanoporous gyroid SiO₂ can be fabricated using hydrolyzed PS–PLLA blends as a template for sol–gel reaction followed by removal of the PS matrix

Surface PEGylation of Silver Nanoparticles: Kinetics of Simultaneous Surface Dissolution and Molecular Desorption

A quantitative study of the stability of silver nanoparticles (AgNPs) conjugated with thiolated polyethylene glycol (SH-PEG) was conducted using gas-phase ion-mobility and mass analyses. The extents of aggregation and surface dissolution of AgNPs, as well as the amount of SH-PEG adsorption and desorption, were able to be characterized simultaneously for the kinetic study. The results show that the SH-PEG with a molecular mass of 6 kg/mol (SH-PEG6K) was able to adsorb to the surface of AgNP to form PEG6K-HS-AgNP conjugates, with the maximum surface adsorbate density of ∼0.10 nm^–2. The equilibrium binding constant for SH-PEG6K on AgNPs was calculated as ∼(4.4 ± 0.9) × 10⁵ L/mol, suggesting a strong affinity due to thiol bonding to the AgNP surface. The formation of SH-PEG6K corona prevented PEG6K-HS-AgNP conjugates from aggregation under the acidic environment (pH 1.5), but dissolution of core AgNPs occurred following a first-order reaction. The rate constant of Ag dissolution from PEG6K-HS-AgNP was independent of the starting surface packing density of SH-PEG6K on AgNP (σ₀), indicating that the interactions of H⁺ with core AgNP were not interfered by the presence of SH-PEG6K corona. The surface packing density of SH-PEG6K decreased simultaneously following a first-order reaction, and the desorption rate constant of SH-PEG6K from the conjugates was proportional to σ₀. Our work presents the first quantitative study to illustrate the complex mechanism that involves simultaneous aggregation and dissolution of core AgNPs in combination with adsorption and desorption of SH-PEG. This work also provides a prototype method of coupled experimental scheme to quantify the change of particle mass versus the corresponding surface density of functional molecular species on nanoparticles

Helical Phase Driven by Solvent Evaporation in Self-Assembly of Poly(4-vinylpyridine)-<i>block</i>-poly(l‑lactide) Chiral Block Copolymers

A series of chiral block copolymers (BCPs*), poly­(4-vinylpyridine)-<i>block</i>-poly­(l-lactide) (P4VP–PLLA), are synthesized through atom transfer radical polymerization and living ring-opening polymerization. Except for typical microphase-separated phases, such as lamellae (L) and hexagonally packed cylinders (HC), a helical phase (H*) with hexagonally packed PLLA helices in a P4VP matrix can be found in the self-assembly of P4VP–PLLA BCPs*, reflecting the chirality effect on BCP self-assembly. The H* formation is strongly dependent upon the solvent evaporation rate for solution casting at which fast evaporation gives the H* phase and slow evaporation results in the HC phase. To further examine the metastability of the H* phase associated with the dynamics of BCP* chains during self-assembly, P4VP–PLLA BCPs* having different molecular weights at a constant composition are utilized for self-assembly. Under the same evaporation rate for solution casting, the H* phase can be obtained in high-molecular-weight P4VP–PLLA BCP* whereas a stable HC phase is found in low-molecular-weight P4VP–PLLA BCP*, indicating the kinetic origin of H* formation due to the long and highly entangled chains in solution for self-assembly. Consequently, the H* phase can be driven by solvent evaporation through a kinetically trapped process and is regarded as a long-lived metastable phase

Quantifying Nanosheet Graphene Oxide Using Electrospray-Differential Mobility Analysis

We report a high-resolution, traceable method to quantify number concentrations and dimensional properties of nanosheet graphene oxide (N-GO) colloids using electrospray-differential mobility analysis (ES-DMA). Transmission electron microscopy (TEM) was employed orthogonally to provide complementary data and imagery of N-GOs. Results show that the equivalent mobility sizes, size distributions, and number concentrations of N-GOs were able to be successfully measured by ES-DMA. Colloidal stability and filtration efficiency of N-GOs were shown to be effectively characterized based on the change of size distributions and number concentrations. Through the use of an analytical model, the DMA data were able to be converted into lateral size distributions, showing the average lateral size of N-GOs was ∼32 nm with an estimated thickness ∼0.8 nm. This prototype study demonstrates the proof of concept of using ES-DMA to quantitatively characterize N-GOs and provides traceability for applications involving the formulation of N-GOs

Protein–Silver Nanoparticle Interactions to Colloidal Stability in Acidic Environments

We report a kinetic study of Ag nanoparticles (AgNPs) under acidic environments (i.e., pH 2.3 to pH ≈7) and systematically investigate the impact of protein interactions [i.e., bovine serum albumin (BSA) as representative] to the colloidal stability of AgNPs. Electrospray-differential mobility analysis (ES-DMA) was used to characterize the particle size distributions and the number concentrations of AgNPs. Transmission electron microscopy was employed orthogonally to provide visualization of AgNPs. For unconjugated AgNPs, the extent of aggregation, or the average particle size, was shown to be increased significantly with an increase of acidity, where a partial coalescence was found between the primary particles of unconjugated AgNP clusters. Aggregation rate constant, <i>k</i>_D, was also shown to be proportional to acidity, following a correlation of log­(<i>k</i>_D) = −1.627­(pH)–9.3715. Using ES-DMA, we observe BSA had a strong binding affinity (equilibrium binding constant, ≈ 1.1 × 10⁶ L/mol) to the surface of AgNPs, with an estimated maximum molecular surface density of ≈0.012 nm^–2. BSA-functionalized AgNPs exhibited highly-improved colloidal stability compared to the unconjugated AgNPs under acidic environments, where both the acid-induced interfacial dissolution and the particle aggregation became negligible. Results confirm a complex mechanism of colloidal stability of AgNPs: the aggregation process was shown to be dominant, and the formation of BSA corona on AgNPs suppressed both particle aggregation and interfacial dissolution of AgNP samples under acidic environments

Handedness of Twisted Lamella in Banded Spherulite of Chiral Polylactides and Their Blends

Banded spherulite resulting from lamellar twisting due to the imbalanced stresses at opposite fold surfaces can be formed by isothermal crystallization of chiral polylactide and its blends with poly­(ethylene glycol) (PEG). Using a polarized light microscope, the handedness of the twisted lamella in banded spherulite is determined. With the same growth axis along the radial direction as evidenced by wide-angle X-ray diffraction (WAXD) for isothermally crystallized samples at different temperatures, the twisted lamellae of chiral polylactides (poly­(l-lactide) (PLLA) and poly­(d-lactide) (PDLA)) display opposite handedness. The split-type Cotton effect on the CO stretching motion of vibrational circular dichroism (VCD) spectra helps determine the helix handedness (i.e., conformational chirality). The results indicate that the conformational chirality can be defined by the molecular chirality through intramolecular chiral interactions. Moreover, the preferred sense of the lamellar twist in the banded spherulite corresponds to the twisting direction identified by the C–O–C vibration motion of VCD spectra, reflecting the role of intermolecular chiral interactions in the packing of polylactide helices. Similar results are obtained in the blends of chiral polylactides and poly­(ethylene glycol) (PEG, a polymer compatible with polylactide), indicating that the impact of chirality is intrinsic irrespective of the specific crystallization conditions. In contrast to the chiral polylactides, the spectrum of the crystalline stereocomplex that associates PLLA and PDLA shows VCD silence. The spectroscopic results are in line with the morphological observations. No banded spherulites are observed in the stereocomplex crystallites due to the symmetric packing of mirror L- and D-chain conformations in the fold surfaces and the crystallites core