Stimuli-responsive degradable silica nanoparticles (NPs) are active topics of nanomaterial research, because they are expected to be low health-risk nanocarriers capable of controlled release of drugs. Among various stimuli-responsive silica NPs, disulfide bond-containing NPs show degradability by glutathione reduced form (GSH). Here, we synthesized and characterized three kinds of thiol-organosilica NPs made from 3-mercaptopropyltrimethoxysilane (MPMS) and 3-mercaptopropyl(dimethoxy)methylsilane (MPDMS). MPMS NPs, MPDMS NPs, and MPMS–MPDMS hybrid NPs revealed that the abundance ratio of disulfide bonds to thiols increased with the increase in content rate of MPDMS in thiol-organosilica NPs. We also revealed that thiol-organosilica NPs, which have disulfide bonds, are GSH-responsive degradable silica NPs using an electron microscopy and Ellman’s tests. Furthermore, we synthesized fluorescent MPMS–MPDMS NPs, including rhodamine B, and demonstrated the GSH-responsive release of dye from the NPs. These experiments indicate the potential of thiol-organosilica NPs, which have disulfide bonds as a GSH-responsive drug carrier.

The extrinsic indentation size effect (ISE) is utilized to analyze the depth-dependent hardness for Berkovich indentation of non-uniform dislocation distributions with one and two dimensional deformation gradients and is then extended to indentation results at grain boundaries. The role of the Berkovich pyramid orientation and placement relative to the grain boundary on extrinsic ISE is considered in terms of slip transmission at yield and plastic incompatibility during post-yield deformation. The results are interpreted using a local dislocation hardening mechanism originally proposed by Ashby, combined with the Hall–Petch equation. The Hall–Petch coefficient determined from the extrinsic ISE of the grain boundary is found to be consistent with the published values for pure Fe and mild steel. A simple, linear continuum strain gradient plasticity model is used to further analyze the results to include contributions from a non-uniform distribution in plastic strain and dislocation density.

Influence of boron nitride (BN) addition in commercially pure titanium (Cp-Ti) was characterized for their microstructural variation, hardness, and oxidation kinetics. Feedstock powders, Cp-Ti with 3 wt% BN (3BN) and 6 wt% BN (6BN), were prepared by roller mill followed by additive manufacturing using laser engineered net shaping (LENS™). Rate of oxidation was measured from thermogravimetric analysis (TGA) at 1000 °C for 50 h. Average instantaneous parabolic constants (kp) for Cp-Ti, 3BN, and 6BN were 41.2 ± 12.0, 28.6 ± 2.8, and 18.2 ± 9.2 mg2/(cm4 h), respectively. Cp-Ti displayed acicular α-Ti microstructure. After TGA, large equiaxed grains along with TiO2 formation at the grain boundaries were observed, which increased the hardness. With BN addition, plate-like TiN and needle-like TiB secondary phases were also observed. Hardness for Cp-Ti, 3BN, and 6BN were 256.9 ± 7.7, 424.0 ± 33.6, and 548.3 ± 49.7 HV0.2, respectively. Overall, a small addition of BN was effective in improving the oxidation resistance of Cp-Ti.

Achieving high fracture toughness and maintaining high strength at the same time are main goals in materials science. In this work, scale-bridging fracture experiments on ultrafine-grained chromium (UFG, Cr) are performed at different length scales, starting from the macroscale over the microscale (in situ SEM) down to the nanoscale (in situ TEM). A quantitative assessment of the fracture toughness yields values of ∼3 MPa m1/2 in the frame of linear elastic fracture mechanics (LEFM) for the macrosamples. The in situ TEM tests reveal explicitly the occurrence of dislocation emission processes involved in energy dissipation and crack tip blunting serving as toughening mechanisms before intercrystalline fracture in UFG body-centered cubic (bcc) metals. In relation to coarse-grained Cr, in situ TEM tests, in this work, demonstrate the importance of strengthening grain boundaries as promising strategy in promoting further ductility and toughening in UFG bcc metals.

Nanoscale models are very small but involve multiple physics, multiscales, confinement, high rates, etc. These make the numerical simulation of intrinsic and extrinsic size effects difficult for the ferrite/cementite layered structure of carbon steel. In this work, a “new” simulation approach is proposed with “hypothesis” as the key to make the on-going simulation simple, physically sound, and the related atomistically based simulation productive. Using this refreshed approach, which is based on the traditional scientific philosophy, size effects that are related to interface structure and the layer thickness on failure due to thermomechanical coupling are investigated. Among interesting findings, it proves that the peak stress in the strain–stress curve as the characteristic parameter to describe the size effects on failure of thermomechanical coupling is not fully accurate, and a multiplication form of energy barrier with fast decaying function of thermal activation energy should be used in the size-dependent failure initiation criterion. This makes developing guidelines available for designing interface sizes at nanoscale.

Grain size effect on twin thickness has been rarely investigated, especially when the grain size is less than 1000 nm. In our previous work (Mater. Sci. Eng.A527, 3942, 2010), different severe plastic deformation techniques were used to achieve a wide range of grain sizes from about 3 μm to 70 nm in a Cu–30% Zn alloy. Transmission electron microscopy (TEM) revealed a gradual decrease in the deformation twin thickness with decreasing grain size. In the present work, high-resolution TEM was used to further identify deformation twins and measure their thickness, especially for grain sizes below 70 nm. The twin thickness was found to gradually reduce with decreasing grain size, until a critical size (20 nm), below which only stacking faults were observed. Interestingly, the relationship between twin thickness and grain size in the ultrafine/nanocrystalline regime is found similar to that in the coarse-grained regime, despite the differences in their twinning mechanisms. This work provides a large set of data for setting up a model to predict the twin thickness in ultrafine-grained and nanocrystalline face-centered cubic materials.