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We investigate vapor-liquid nucleation and subsequent freezing of aqueous-alcohol nanodroplets containing 1-pentanol, 1-hexanol, and their 3-isomers. The aerosols are produced in a supersonic nozzle, where condensation and freezing are characterized by static pressure and Fourier transform Infrared (FTIR) spectroscopy measurements. At fixed water concentrations, the presence of alcohol enables particle formation at higher temperatures since both the equilibrium vapor pressure above the critical clusters and the cluster interfacial free energy are decreased relative to the pure water case. The disappearance of a small free OH peak, observed for pure water droplets, when alcohols are added and shifts in the CH peaks as a function of alcohol chain length reveal varying surface partitioning preferences of the alcohols. Changes in the FTIR spectra during freezing, as well as changes in the ice component derived from self-modeling curve resolution analysis, show that 1-hexanol and 1-pentanol perturb freezing less than their branched isomers do. This behavior may reflect the molecular footprints of the alcohols, the available surface area of the droplets, and not only alcohol solubility. The presence of alcohols also lowers the freezing temperature relative to that of pure water, but when there is clear evidence for the formation of ice, the ice nucleation rates change by less than a factor of ∼2-3 for all cases studied.

We generate water-rich aerosols containing 1-propanol and 1-pentanol in a supersonic nozzle to study the effects of these solutes on the freezing behavior of water. Condensation and freezing are characterized by two complementary techniques, pressure trace measurements and Fourier Transform Infrared spectroscopy. When 1-pentanol and 1-propanol are present, condensation occurs at higher temperatures because particle formation from the vapor phase is enhanced by the decrease in interfacial free energy of mixed aqueous-alcohol critical clusters relative to those of pure water. FTIR results suggest that when ∼6 nm radius droplets freeze, the tetrahedral structure of the ice is well preserved up to an overall alcohol mole fraction of 0.031 for 1-propanol and 0.043 for 1-pentanol. In this concentration range, the ice nucleation temperature decreases continuously with increasing 1-propanol concentration, whereas the onset of freezing is not significantly perturbed by 1-pentanol up to a mole fraction of 0.03. Furthermore, once freezing starts the ice nucleation rates in the aqueous-alcohol droplets are very close to those for pure water. In contrast, at the highest mole fractions of either alcohol it is not clear whether droplets freeze to form crystalline ice since the final state of the particles cannot be adequately characterized with the available experimental techniques.

The formation of subcritical methanol clusters in the vapor phase is known to complicate the analysis of nucleation measurements. Here, we investigate how this process affects the onset of binary nucleation as dilute water–methanol mixtures in nitrogen carrier gas expand in a supersonic nozzle. These are the first reported data for water–methanol nucleation in an expansion device. We start by extending an older monomer–dimer–tetramer equilibrium model to include larger clusters, relying on Helmholtz free energy differences derived from Monte Carlo simulations. The model is validated against the pressure/temperature measurements of Laksmono et al. [Phys. Chem. Chem. Phys. 13, 5855 (2011)] for dilute methanol–nitrogen mixtures expanding in a supersonic flow prior to the appearance of liquid droplets. These data are well fit when the maximum cluster size imax is 6–12. The extended equilibrium model is then used to analyze the current data. On the addition of small amounts of water, heat release prior to particle formation is essentially unchanged from that for pure methanol, but liquid formation proceeds at much higher temperatures. Once water comprises more than ∼24 mol % of the condensable vapor, droplet formation begins at temperatures too high for heat release from subcritical cluster formation to perturb the flow. Comparing the experimental results to binary nucleation theory is challenged by the need to extrapolate data to the subcooled region and by the inapplicability of explicit cluster models that require a minimum of 12 molecules in the critical cluster.

As nanomaterials move toward commercial applications, methods of scalable, solution-based manufacturing of polymer nanoparticles are increasingly important. Flash nanoprecipitation (FNP) is a popul...

Studies of vapor phase nucleation have largely been restricted to one of two limiting cases—nucleation controlled by a substantial free energy barrier or the collisional limit where the barrier is negligible. For weakly bound systems, exploring the transition between these regimes has been an experimental challenge, and how nucleation evolves in this transition remains an open question. We overcome these limitations by combining complementary Laval expansion experiments, providing new particle formation data for carbon dioxide over a uniquely broad range of conditions. Our experimental data together with a kinetic model using rate constants from high-level quantum chemical calculations provide a comprehensive picture of new particle formation as nucleation transitions from a barrier-dominated process to the collisional limit.

The condensation of carbon dioxide (CO2) is a topic of general interest in view of global decarbonization targets, e.g. in low-temperature CO2 capture technologies promoting the phase transition of CO2 gas is the crucial step. Homogeneous nucleation of a mixture of CO2 and argon gas in a supersonic nozzle has been studied at temperatures from 78 to 92 K, and CO2 partial pressures between 70 and 800 Pa. The consistency between the current data and measurements at higher temperature suggests the critical clusters remain liquid-like even at these low temperatures.Here we present large-scale atomistic molecular dynamics (MD) simulations of homogenous CO2 nucleation from the vapour phase at temperatures from 75 to 105 K. The MD approach is an unbiased method to study the nucleation process, including the phase and structure of even the smallest clusters. We used argon carrier gas as a heat bath for the CO2 molecules to avoid unphysical removal of latent heat.Simulations confirm that despite strong undercooling, nucleation proceeds through liquid-like clusters. Also, by applying standard steady-state cluster growth kinetics, we are able to calculate the cluster formation free energies from the MD simulations. The results suggest a curvature correction to the classical liquid drop model used in the classical nucleation theory. The correction depends only on the bulk liquid properties, and hence the simulation-based correction can be applied to predict the nucleation rates of real CO2.The simulation-based theory is able to capture the magnitude and the temperature-dependency of the nucleation rate rather well, whereas both standard CNT and its self-consistent version (SCNT) underestimate the rate by several orders of magnitude. Here we have corrected the theoretical values with the non-isothermal factor, which is about 0.01-0.1 for the studied system.

Large scale molecular dynamics simulations of the homogeneous nucleation of carbon dioxide in an argon atmosphere were carried out at temperatures between 75 and 105 K. Extensive analyses of the nucleating clusters' structural and energetic properties were performed to quantify these details for the supersonic nozzle experiments described in the first part of this series [Dingilian et al., Phys. Chem. Chem. Phys., 2020, 22, 19282-19298]. We studied ten different combinations of temperature and vapour pressure, leading to nucleation rates of 10(23)-10(25) cm(-3) s(-1). Nucleating clusters possess significant excess energy from monomer capture, and the observed cluster temperatures during nucleation - on both sides of the critical cluster size - are higher than that of the carrier gas. Despite strong undercooling with respect to the triple point, most clusters are clearly liquid-like during the nucleation stage. Only at the lowest simulation temperatures and vapour densities, clusters containing over 100 molecules are able to undergo a second phase transition to a crystalline solid. The formation free energies retrieved from the molecular dynamics simulations were used to improve the classical nucleation theory by introducing a Tolman-like term into the classical liquid-drop model expression for the formation free energy. This simulation-based theory predicts the simulated nucleation rates perfectly, and improves the prediction of the experimental rates compared to self-consistent classical nucleation theory.

Using molecular dynamics simulation of octane (C8) and nonadecane (C19), we probe the mechanism of n-alkane surface freezing, the appearance of a crystalline monolayer above the liquid at a temperature Tsf above the bulk freezing point Tf. Formation of a crystalline monolayer occurs robustly in these systems. When Tf > Tsf, the surface frozen phase is metastable with respect to the solid but persists for long periods for study in simulations. Surface freezing of both C8 and C19 is driven by significant energy-lowering when alkane chains become ordered along the surface normal, and we elucidate the origins of this phenomenon. The degree of configurational disorder in the surface frozen layer relative to the solid is much larger for C8 compared to C19. From the Gibbsian viewpoint, we extract the excess energy and entropy of the liquid and surface frozen phases. We also consider the surface frozen layer as an intervening third phase, the viewpoint taken in previous theoretical analyses. Here, we find significantly increased entropy of the surface frozen phase of C8 associated with configurational disorder, while the energy and entropy of the surface frozen phase of C19 are marginally different from the bulk solid. Finally, by combining our previously determined solid–vapor surface free energies of C8 and C19 with liquid–vapor surface tensions from this work, we eliminate wetting as a possible mechanism for C8 surface freezing, but it remains a possibility for C19. We analyze the molecular structure of the liquid, surface frozen, and solid surfaces and discuss its relevance to thermodynamic properties.

We studied the homogeneous nucleation of carbon dioxide in the carrier gas argon for concentrations of CO(2)ranging from 2 to 39 mole percent using three experimental methods. Position-resolved pressure trace measurements (PTM) determined that the onset of nucleation occurred at temperatures between 75 and 92 K with corresponding CO(2)partial pressures of 39 to 793 Pa. Small angle X-ray scattering (SAXS) measurements provided particle size distributions and aerosol number densities. Number densities of approximately 10(12)cm(-3), and characteristic times ranging from 6 to 13 mu s, resulted in measured nucleation rates on the order of 5 x 10(17)cm(-3)s(-1), values that are consistent with other nucleation rate measurements in supersonic nozzles. Finally, we used Fourier transform infrared (FTIR) spectroscopy to identify that the condensed CO(2)particles were crystalline cubic solids with either sharp or rounded corners. Molecular dynamics simulations, however, suggest that CO(2)forms liquid-like critical clusters before transitioning to the solid phase. Furthermore, the critical clusters are not in thermal equilibrium with the carrier gas. Comparisons with nucleation theories were therefore made assuming liquid-like critical clusters and incorporating non-isothermal correction factors.

Acid-degradable polymers are well-suited for use as drug delivery vehicles because numerous physiological sites (e.g., intracellular endocytic pathway) are acidic. Here we report the synthesis of acid-sensitive silylated polysaccharides derived from either dextran or inulin with various alkyl substitutions on the silicon center: trimethylsilyl dextran (TMS-DEX), ethyldimethylsilyl dextran (EDMS-DEX), triethylsilyl dextran (TES-DEX), and trimethylsilyl inulin (TMS-IN). The silylated dextran (Silyl-DEX) and silylated inulin (Silyl-IN) polymers were fabricated into microparticles (MPs) via emulsification followed by solvent evaporation. These MPs were relatively stable at extracellular pH 7.4 and displayed a wide range of pH 2.0 and 5.0 degradation half-lives (fifteen minutes to greater than nine days) that were dependent on the extent of silylation (40 to 98%) and steric crowding on the silicon center (trimethyl to ethyldimethyl to triethyl). Silyl-DEX and Silyl-IN MPs exhibited cytocompatibility when cultured in vitro with RAW 264.7 macrophages. TES-DEX and TMS-IN MPs, composed of highly hydrophobic moieties and the parent immunostimulatory inulin, respectively, elicited substantial in vitro production of tumor necrosis factor alpha, a cytokine associated with an innate immune response. In vivo immunization with a model ovalbumin antigen encapsulated in silylated polysaccharide MPs, without a separate adjuvant, resulted in a dual humoral and cellular response that was superior to an alum-adjuvanted formulation. Overall, we present Silyl-DEX and Silyl-IN as members of the acid-degradable polymer family for potential use in subunit vaccines and other drug delivery applications.

Hypothesis Elongated micelles may be preferred over spherical because of their increased loading capacity, differential mass transport and biodistribution. Although morphological transitions of block co-polymer (BCP) micelles have been extensively investigated in batch systems, research on continuous or semi-continuous scalable approaches such as flash nanoprecipitation and coaxial electrospray-enabled interfacial instability (Aero-IS) have primarily focused on producing spherical micelles. This paper investigates whether process changes intended to increase micelle production via Aero-IS also induce morphological transitions. Experiments BCP micelles were synthesized from carboxylated polystyrene-block-poly(ethylene oxide) (PS-b-PEO) (PS 9.5 kDa:PEO 18.0 kDa) using Aero-IS. Volumetric flowrates, polymer concentrations, and emulsion temperature were varied to investigate their effect on the micelle production rate and resulting micelle structure, including transitions to worm-like micelles. Findings These findings report the first worm-like micelles formed via a scalable, interfacial instability approach. The morphological transitions obtained by increasing polymer concentration occurred at lower nominal values than in corresponding batch processes. Optimizing operating conditions also led to a 12-fold increase in micelle production rates over prior electrospray reports (Duong, 2014). Thus, the Aero-IS approach holds promise for scalable nanomanufacturing of worm-like micelles, potentially enabling applications in drug delivery, imaging, diagnostics, and separations.

Purpose Poly(lactic-co-glycolic acid) (PLGA) is widely used for drug delivery because of its biocompatibility, ability to solubilize a wide variety of drugs, and tunable degradation. However, achieving sub-100 nm nanoparticles (NPs), as might be desired for delivery via the enhanced permeability and retention effect, is extremely difficult via typical top-down emulsion approaches. Methods Here, we present a bottom-up synthesis method yielding PLGA/block copolymer hybrids (ie, "PolyDots"), consisting of hydrophobic PLGA chains entrapped within self-assembling poly(styrene-b-ethylene oxide) (PS-b-PEO) micelles. Results PolyDots exhibit average diameters

Whether crystallization starts at the liquid-vapor interface or randomly throughout the bulk has been the subject of intense debate. In our earlier work, we investigated the freezing of supercooled nanodroplets of short chain (C8, C9) n-alkanes formed by homogeneous condensation in a supersonic nozzle. The rate at which the solid appeared suggested freezing starts at the droplet surface well before the rest of the droplet freezes. Experiments were, however, limited to a single condition for each compound and it was not clear whether freezing of n-alkanes always occurs in this two step manner. Here, we expand our work to include freezing of a third n-alkane, n-decane, and, furthermore, we vary the temperatures at which droplets are formed and freeze. The phase transitions are again characterized using three experimental techniques - pressure trace measurements (PTM), Fourier Transform Infrared Spectroscopy (FTIR), and Small Angle X-ray Scattering (SAXS). We also use Wide Angle X-ray Scattering (WAXS) to confirm, for the first time, the crystalline nature of our frozen n-alkane nanodroplets. As the temperature at which the droplets form and freeze decreases, the kinetics of the phase transition changes. At higher temperatures, the phase transition occurs in two steps characterized by different rates, whereas at lower temperatures we observe only a single step. Finally, in the lowest temperature experiment, where droplets start to form and freeze ∼50 K below the bulk melting temperature, we found that the particles develop a fractal structure and appear locked in a "frustrated" crystalline state.

The classical picture invoked for heterogeneous nucleation is frequently that of a liquid condensing onto an immiscible solid particle. Here, we examine heterogeneous nucleation of CO2 onto particles comprised of n-pentane or n-hexane under conditions where CO2 should be a solid and the seed particles may be liquid or solid. Although CO2 condensed under all but one of the six conditions investigated, these experiments do not easily fit into the framework of standard heterogeneous nucleation experiments. Rather they explore unconventional regimes of heterogeneous nucleation in which the state of the seed particle may both affect whether deposition can proceed, and, in turn, be influenced by the presence of the condensing species. The work complements the earlier work of Tanimura et al. [RSC Adv., 2015, 5, 105537-105550] that investigated CO2 condensation onto ice nanoparticles, by using seed particles comprised of non-polar compounds that form and freeze under conditions where CO2 is already supersaturated with respect to the solid ice. In some cases, the conditions for seed formation approach the limit of homogeneous CO2 nucleation. Vibrational spectroscopy measurements help pinpoint where CO2 starts to condense. Furthermore, these IR measurements suggest that the n-alkanes never freeze in the presence of CO2, even if the temperatures are well below those required for them to freeze when CO2 is absent. Over the temperature range 65T/K140, the conditions corresponding to the onset of CO2 heterogeneous nucleation on pre-existing seed particle almost all lie very close to the extrapolated vapor-liquid equilibrium line of CO2 for a broad range of seed materials.