Alexei V. Tivanski

Atmospheric aerosol viscosity governs diffusion time scales of reactive gases into aerosols, thereby influencing gas uptake, heterogeneous chemistry, and atmospheric aging. However, direct viscosity measurements of individual semisolid aerosols have been restricted to a relatively high viscosity range and submicrometer size. Herein, a new atomic force microscopy-based nanorheological experimental approach is presented that utilizes force–indentation distance and indentation rate measurements at varying cantilever velocities to quantify the viscosity of individual semisolid aerosols as a function of relative humidity (RH). Using glucose and sucrose as model systems, we demonstrate accurate single particle viscosity quantification spanning ∼102·5 to 107 Pa s under atmospherically relevant RH conditions. We establish an iterative cantilever velocity framework that enables the determination of the appropriate velocity required for accurate viscosity characterization of aerosols without prior knowledge of their composition. Additionally, we demonstrate that the method enables accurate viscosity quantification of individual sub-100 nm aerosols. We anticipate that future viscosity measurements of atmospheric aerosols from various sources at different RHs will provide valuable insights into aerosol viscosity variability and reveal the extent of particle-to-particle heterogeneity.

Here we investigate the effects of crystal size on the mechanical properties (Young’s modulus, framework flexibility) of a switchable metal–organic framework (MOF): zeolitic imidazolate framework-90 (ZIF-90) individual crystals with sizes ranging from micro- to nanodimensions. Atomic force microscopy (AFM) nanoindentation measurements over individual crystals reveal a significant reduction in Young’s modulus with crystal-size reduction that follows a continuous power-law relationship, where Young’s modulus decreases by nearly 1 order of magnitude as crystal base size decreases from ∼5 to 0.4 μm. Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) analyses coupled with the AFM results reveal that the origin of the size-dependent framework flexibility is primarily attributed to an increased concentration of missing metal node defects for smaller crystals. The presence of missing metal node defects in ZIF-90 crystals was further confirmed by single-crystal optical photothermal infrared spectroscopy measurements. Significantly, the value of the power-law exponent in Young’s modulus versus crystal-size data was related to the magnitude of the relative increase in the number of missing metal node defects, indicating that the extent of the framework flexibility change with crystal size can in part be attributed to the rate of defect accumulation with crystal downsizing at the nanoscale. These findings indicate that the power-law scaling of mechanical properties may serve as an approach to assess the size-dependent extent of point-defect evolution in switchable MOFs, potentially enabling a rational design of solids with controlled functional properties.

A rock tumbler outfitted with LED lights allows for mechanochemical preparation of photoactive cocrystals.

This study investigates the effects of wind speed on physicochemical properties such as water uptake, phase state, and viscosity at varying relative humidity (RH) of individual nascent sea spray aerosols (SSAs). We examined SSA sized within 0.1−0.6 μm generated from a wind-wave channel at two wind speeds: 10 m/s representing a wind lull scenario over the ocean and 19 m/s corresponding to wind speeds encountered in stormy conditions. Atomic force microscopy (AFM) was utilized to study two predominant SSA morphologies: core−shell and rounded. AFM phase state measurements at 60% RH revealed that shells of core−shells at 19 m/s were largely liquid, while those at 10 m/s were mostly semisolid or liquid with similar proportions, where semisolid shells exhibited higher viscosities at lower wind speed. Rounded SSAs were predominantly liquid or semisolid at 60% RH, with similar semisolid viscosities for both wind speeds. Increased water uptake was observed for core−shells at 19 m/s, while rounded SSA had similar hygroscopicity between the two wind conditions. Collectively, we observed a variation in the physicochemical properties of SSA generated at two wind speeds, which can be attributed to the impact of elevated wind speed on disrupting the sea surface microlayer film structure and composition.

Radiation therapy is a standard of care treatment for patients with glioblastoma. However, patients’ survival rate is dismal, with nearly all patients experiencing disease progression after treatment. Enriched iron content associated with increased transferrin receptor (TfR) expression is an indicator of poor glioblastoma patient outcomes; however, the underlying contributions to tumor progression remain elusive. The goal of this present study is to understand how iron metabolism in glioma contributes to radiation-induced glioblastoma cell motility. U251 and a doxycycline-inducible ferritin heavy chain overexpressing U251 (U251 FtH⁺) cell line were used. For in vitro studies, cells were irradiated with 2 Gy using a ³⁷Cs source, and after 72 h, atomic force microscopy (AFM) nanoindentation was employed to assess changes in cell stiffness following irradiation. Cell motility was studied using temporal confocal microscopy. For in vivo studies, U251 cells were grown in the rear flanks of female nude athymic mice, and the tumor was irradiated with five fractions of 2 Gy (10 Gy). The tumors were then imaged using a GE 7T small animal MRI to assess changes in T2* MRI, and colorimetric analysis of labile iron was performed using ferrozine. Following irradiation, a biomechanical shift characterized by decreased cell stiffness along with increased cell motility occurred in U251 cells, which corresponded to increased TfR expression. FtH overexpression completely reversed the enhanced cell motility following irradiation. Irradiation of U251 tumors induced the same iron metabolic shift. Interestingly, the change in labile iron in U251 tumors corresponded with an increase in T2* relaxation times, suggesting that T2* mapping may serve as a surrogate marker for assessing radiation-induced changes in iron metabolism.

The exploitation of noncovalent bonding in the solid state is attractive to generate one‐dimensional (1D) wire‐like assemblies of metals and uncover dynamic and physical properties of such intriguing structures. Herein, we describe a metal‐organic crystal based on Ag(I) ions that assemble to be organized into 1D wire‐like assemblies maintained by argentophilic interactions. UV‐light irradiation of the crystal composed of the 1D structures results in a single‐crystal‐to‐single‐crystal (SCSC) photodimerization that transforms the 1D periodic metal arrays to isolated metal dimers. The structural reconfiguration creates small voids in the crystal and the resulting solids exhibit a substantial increase in softness up to 60%.

Sea spray aerosol (SSA) represents one of the most abundant natural aerosol types, contributing significantly to global aerosol mass and aerosol optical depth, as well as to both the magnitude of and the uncertainty in aerosol radiative forcing. In addition to its direct effects, SSA can also serve as ice-nucleating particles (INPs), which are required for the initiation of cloud glaciation at temperatures warmer than ca. −36 °C. This study presents initial results from the CHaracterizing Atmosphere-Ocean parameters in SOARS (CHAOS) mesocosm campaign, which was conducted in the new Scripps Ocean-Atmosphere Research Simulator (SOARS) wind–wave channel. SOARS allows for isolation of individual factors, such as wave height, wind speed, water temperature, or biological state, and can carefully vary them in a controlled manner. Here, we focus on the influence of wind speed on the emission of SSA and INPs. In agreement with recent Southern Ocean measurements, online INP concentrations during CHAOS showed an increasing relationship with wind speed, whereas offline CHAOS INP concentrations did not, which may be related to sampling inlet differences. Changes in the INP activated fraction, dominant INP particle morphology, and INP composition were seen to vary with wind. Seawater ice-nucleating entity concentrations during CHAOS were stable over time, indicating that changes in atmospheric INPs were driven by wind speed and wave-breaking mechanics rather than variations in seawater chemistry or biology. While specific emission mechanisms remain elusive, these observations may help explain some of the variability in INP concentration and composition that has been seen in ambient measurements.

Sea spray aerosol (SSA) represent one of the most abundant natural aerosol types, contributing significantly to global aerosol mass and aerosol optical depth, as well as to both the magnitude and uncertainty of aerosol radiative forcing. In addition to their direct effects, SSA can also serve as ice nucleating particles (INPs), which are required for the initiation of cloud glaciation at temperatures warmer than ∼-36 °C. This study presents initial results from the CHaracterizing Atmosphere-Ocean parameters in SOARS (CHAOS) mesocosm campaign, which was conducted in the new Scripps Ocean-Atmosphere Research Simulator (SOARS) wind-wave channel at the Scripps Institution of Oceanography. SOARS allows for isolation of individual factors, such as wave height, wind speed, water temperature, or biological state, and can carefully vary them in a controlled manner. Here, we focus on the influence of wind speed on the emission of SSA and INPs. Unlike recent measurements from the Southern Ocean, real-time and offline INP observations during CHAOS exhibited opposite relationships with wind speed, which may be related to sampling inlet differences. Changes in the INP activated fraction, dominant INP particle morphology, and INP composition were seen to vary with wind. Seawater ice nucleating entity concentrations during CHAOS were stable over time, indicating changes in atmospheric INPs were driven by wind speed and wave-breaking mechanics rather than variations in seawater chemistry or biology. While specific emission mechanisms remain elusive, these observations may help explain some of the variability in INP concentration and composition that have been seen in ambient measurements.

Sea spray aerosol (SSA) represent one of the most abundant natural aerosol types, contributing significantly to global aerosol mass and aerosol optical depth, as well as to both the magnitude and uncertainty of aerosol radiative forcing. In addition to their direct effects, SSA can also serve as ice nucleating particles (INPs), which are required for the initiation of cloud glaciation at temperatures warmer than ∼-36 °C. This study presents initial results from the CHaracterizing Atmosphere-Ocean parameters in SOARS (CHAOS) mesocosm campaign, which was conducted in the new Scripps Ocean-Atmosphere Research Simulator (SOARS) wind-wave channel at the Scripps Institution of Oceanography. SOARS allows for isolation of individual factors, such as wave height, wind speed, water temperature, or biological state, and can carefully vary them in a controlled manner. Here, we focus on the influence of wind speed on the emission of SSA and INPs. Unlike recent measurements from the Southern Ocean, real-time and offline INP observations during CHAOS exhibited opposite relationships with wind speed, which may be related to sampling inlet differences. Changes in the INP activated fraction, dominant INP particle morphology, and INP composition were seen to vary with wind. Seawater ice nucleating entity concentrations during CHAOS were stable over time, indicating changes in atmospheric INPs were driven by wind speed and wave-breaking mechanics rather than variations in seawater chemistry or biology. While specific emission mechanisms remain elusive, these observations may help explain some of the variability in INP concentration and composition that have been seen in ambient measurements.

Sea spray aerosol (SSA) represent one of the most abundant natural aerosol types, contributing significantly to global aerosol mass and aerosol optical depth, as well as to both the magnitude and uncertainty of aerosol radiative forcing. In addition to their direct effects, SSA can also serve as ice nucleating particles (INPs), which are required for the initiation of cloud glaciation at temperatures warmer than ∼-36 °C. This study presents initial results from the CHaracterizing Atmosphere-Ocean parameters in SOARS (CHAOS) mesocosm campaign, which was conducted in the new Scripps Ocean-Atmosphere Research Simulator (SOARS) wind-wave channel at the Scripps Institution of Oceanography. SOARS allows for isolation of individual factors, such as wave height, wind speed, water temperature, or biological state, and can carefully vary them in a controlled manner. Here, we focus on the influence of wind speed on the emission of SSA and INPs. Unlike recent measurements from the Southern Ocean, real-time and offline INP observations during CHAOS exhibited opposite relationships with wind speed, which may be related to sampling inlet differences. Changes in the INP activated fraction, dominant INP particle morphology, and INP composition were seen to vary with wind. Seawater ice nucleating entity concentrations during CHAOS were stable over time, indicating changes in atmospheric INPs were driven by wind speed and wave-breaking mechanics rather than variations in seawater chemistry or biology. While specific emission mechanisms remain elusive, these observations may help explain some of the variability in INP concentration and composition that have been seen in ambient measurements.