Application of Sublimation in the Synthesis and Crystal Growth of Organosulfones.

The solvent-free elimination of sulfinic acid and aromatization of 1,6-trans-substituted bis(arylsulfone) trienes is reported. It is shown that sublimation can be used as a 'green' method to combine the thermal transformation of six trienes and the crystal growth of the resulting 4-(phenylsulfonyl)biphenyls. When the sublimation conditions are carefully controlled, high quality single crystals of the 4-(phenylsulfonyl)biphenyls are obtained. Theoretical modelling of the reaction using the simplified triene Ph-(CH)6-SO2H showed that the cyclization is energetically feasible and that the complete conversion is possible during the timescale of the sublimation. At temperatures slightly higher than the optimum sublimation temperature two of the trienes transformed into 1,4-cyclohexadienes that did not eliminate phenylsulfinic acid. A reaction mechanism involving a 1,3-hydrogen shift induced by free PhS. radicals is proposed for the formation of the 1,4-cyclohexadienes.

Resultant compound from sublimation test for Gentianae Radix in Japanese Pharmacopoeia was 5-(hydroxymethyl)furfural.

Gentianae Radix, an herbal medicine, has been used as a gastrointestinal drug in Japan. In the Japanese Pharmacopoeia 18th Revision, the sublimation test is specified as an identification test for Gentianae Radix. The compound obtained in this sublimation test was believed to be gentisin, a xanthone family compound. However, the compound we identified using liquid chromatography-high-resolution mass spectrometry (LC-HRMS) and 1H- and 13C-NMR was 5-(hydroxymethyl)furfural (5-HMF). The same compound was found to be a sublimate of Gentianae Scabrae Radix and Gentianae Macrophyllae Radix, belonging to the same genus as Gentianae Radix. These results indicate the necessity to revise the identification test for Gentianae Radix to a more unique method.

Controlled Sublimation Rate of Guest Drug from Polymorphic Forms of a Cyclodextrin-Based Polypseudorotaxane Complex and Its Correlation with Molecular Dynamics as Probed by Solid-State NMR.

Encapsulation of active pharmaceutical ingredients (APIs) in confined spaces has been extensively explored as it dramatically alters the molecular dynamics and physical properties of the API. Herein, we explored the effect of encapsulation on the molecular dynamics and physical stability of a guest drug, salicylic acid (SA), confined in the intermolecular spaces of γ-cyclodextrin (γ-CD) and poly(ethylene glycol) (PEG)-based polypseudorotaxane (PPRX) structure. The sublimation tendency of SA encapsulated in three polymorphic forms of the γ-CD/PEG-based PPRX complex, monoclinic columnar (MC), hexagonal columnar (HC), and tetragonal columnar (TC), was investigated. The SA sublimation rate was decreased by 3.0-6.6-fold and varied in the order of MC form > HC form > TC form complex. The 13C and 1H magic-angle spinning (MAS) solid-state nuclear magnetic resonance (NMR) spectra and 13C spin-lattice relaxation time (T1) indicated that the encapsulated SA molecules existed as the monomeric form, and its molecular mobility increased in the order of MC form > HC form > TC form complex. In the complexes, a rapid chemical exchange between two dynamic states of SA (free and bound) was suggested, with varying adsorption/desorption rates accounting for its distinct molecular mobility. This adsorption/desorption process was influenced by proton exchange at the interaction site and interaction strength of SA in the complexes, as evidenced by 1H MAS spectra and temperature dependency of the 13C carbonyl chemical shift. A positive correlation between the molecular mobility of SA and its sublimation rate was established. Moreover, the molecular mobility of γ-CD and PEG in the complexes coincided with that of SA, which can be explained by fast guest-driven dynamics. This is the first report on the stability improvement of an API through complexation in polymorphic supramolecular host structures. The relationship between the molecular dynamics and physical properties of encapsulated API will aid in the rational design of drug delivery systems.

Pulsão de Morte e Sublimação: A (Re)invenção da Vida nas Dobras da Racionalidade Técnico-Científica / Death Drive and Sublimation: The (Re)invention of Life in the Folds of Technical-Scientific Rationality / Pulsión de Muerte y Sublimación: (Re)invención de la Vida en las Doblas de la Técnica

O advento das biotecnologias no mundo contemporâneo, em particular das Novas Tecnologias Reprodutivas (NTR's), liberando a sexualidade dos antigos imperativos da procriação, nos oferece uma prova contundente da abertura ilimitada da vida à transformação das condições em que as normas vitais engajam os organismos no processo de individuação. Mais do que isso, evidencia o caráter essencialmente contingente da ligação entre vida, morte e sexualidade. O objetivo deste trabalho é examinar a fecundidade da concepção freudiana de sublimação - lida sob o registro das transformações que a ela se impõem com o advento do conceito de pulsão de morte (1920) - em subsidiar uma reflexão ética e política acerca dos efeitos da incidência das Novas Tecnologias Reprodutivas (NTR's) nos campos da reprodução, da sexualidade e do laço social. Nossa hipótese é a de que o fenômeno das biotecnologias desvela, sob a cobertura do temor, tão frequentemente evocado por alguns de nossos contemporâneos, de dilapidação das instituições e dos modos de vida sobre os quais acreditávamos poder fundar nossa fantasmática "humanidade", a infinita potência da vida em recriar-se diante d'isso que quer destruí-la.

The advent of biotechnologies in the contemporary world, particularly New Reproductive Technologies (NTRs), freeing sexuality from the old imperatives of procreation, offers us overwhelming proof of the unlimited opening up of life to the transformation of conditions in which vital norms engage the organisms in the individuation process. Even more so, it highlights the essentially contingent character of the connection between life, death, and sexuality. The aim of this study is, therefore, to examine the fruitfulness of the Freudian conception of sublimation, read under the register of the transformations imposed upon this notion with the advent of the death drive concept (1920), in subsidizing an ethical and political reflection on the effects of the incidence of NTRs in the reproduction, sexuality and social bond fields. Our hypothesis is that the biotechnologies phenomenon reveals, under the cover of fear, so often evoked by some of our contemporaries, of institutional dilapidation and ways of life in which we believed we could establish our fantastic "humanity", the infinite life's power to recreate itself in the face of that which wants to destroy it.

La llegada de las biotecnologías en el mundo contemporáneo, en particular de las Nuevas Tecnologías Reproductivas (NTR's), liberando la sexualidad de los imperativos de la procreación, nos ofrece una prueba contundente de la abertura ilimitada de la vida a la transformación de las condiciones en que las normas vitales capacitan el organismo a la individuación. Más allá de eso, se evidencia el carácter esencialmente contingente de la ligación entre vida, muerte y sexualidad. El objetivo de este estudio es examinar la fecundidad de la concepción freudiana de sublimación - leída bajo el registro de las transformaciones que a ella se imponen con la llegada del concepto de pulsión de muerte (1920) - en subsidiar una reflexión ética y política acerca de los efectos de la incidencia de las Nuevas Tecnologías Reproductivas (NTR's) en los campos de la reproducción, de la sexualidad y del lazo social. Nuestra hipótesis es que el fenómeno de las biotecnologías desvela, bajo la cobertura del temor, tan frecuentemente evocado por algunos de nuestros contemporáneos, de dilapidación de las instituciones y de los modos de vida sobre los cuales creíamos poder fundar nuestra fantasmática "humanidad", la infinita potencia de la vida en recrearse de ante d'eso que quiere destruirla.

The Freeze-Drying of Pharmaceuticals in Vials Nested in a Rack System-Part II: Primary Drying Behaviour.

The freeze-drying of biopharmaceuticals is a common strategy to extend their shelf-life and facilitate the distribution of therapeutics. The drying phase is the most demanding one in terms of energy consumption and determines the overall process time. Our previous work showed how the loading configuration can impact freezing. This paper focuses on primary drying by comparing the thermal behaviour of vials loaded in direct contact with the shelf or nested in a rack system. The overall heat transfer coefficient from the apparatus to the product was evaluated at different chamber pressures (5-30 Pa) and shelf temperatures (from -10 °C to +30 °C), and in the case of various vial positions (central, semi-border, and border vials). Because of the suspended configuration, the heat transfer coefficient was less affected by chamber pressure in vials nested in a rack system. The two loading configurations displayed comparable heat transfer efficiency below 10 Pa. For higher chamber pressure, the heat transfer coefficients of nested vials were lower than those of vials in direct contact with the shelf. Nevertheless, the rack system was beneficial for reducing the inter-vial variability as it promoted higher uniformity in the heat transfer coefficients of central vials. Eventually, thermal image analyses highlighted limited temperature differences between the vials and the rack system.

Surface premelting of ice far below the triple point.

Premelting of ice, a quasi-liquid layer (QLL) at the surface below the melting temperature, was first postulated by Michael Faraday 160 y ago. Since then, it has been extensively studied theoretically and experimentally through many techniques. Existing work has been performed predominantly on hexagonal ice, at conditions close to the triple point. Whether the same phenomenon can persist at much lower pressure and temperature, where stacking disordered ice sublimates directly into water vapor, remains unclear. Herein, we report direct observations of surface premelting on ice nanocrystals below the sublimation temperature using transmission electron microscopy (TEM). Similar to what has been reported on hexagonal ice, a QLL is found at the solid-vapor interface. It preferentially decorates certain facets, and its thickness increases as the phase transition temperature is approached. In situ TEM reveals strong diffusion of the QLL, while electron energy loss spectroscopy confirms its amorphous nature. More significantly, the premelting observed in this work is thought to be related to the metastable low-density ultraviscous water, instead of ambient liquid water as in the case of hexagonal ice. This opens a route to understand premelting and grassy liquid state, far away from the normal water triple point.

Extending the Shelf-Life of Immunoassay-Based Microfluidic Chips through Freeze-Drying Sublimation Techniques.

Point-of-care testing (POCT) platforms utilizing immunoassay-based microfluidic chips offer a robust and specific method for detecting target antibodies, demonstrating a wide range of applications in various medical and research settings. Despite their versatility and specificity, the adoption of these immunoassay chips in POCT has been limited by their short shelf-life in liquid environments, attributed to the degradation of immobilized antibodies. This technical limitation presents a barrier, particularly for resource-limited settings where long-term storage and functionality are critical. To address this challenge, we introduce a novel freeze-dry sublimation process aimed at extending the shelf-life of these microfluidic chips without compromising their functional integrity. This study elaborates on the mechanisms by which freeze-drying preserves the bioactivity of the immobilized antibodies, thereby maintaining the chip's performance over an extended period. Our findings reveal significant shelf-life extension, making it possible for these POCT platforms to be more widely adopted and practically applied, especially in settings with limited resources. This research paves the way for more accessible, long-lasting, and effective POCT solutions, breaking down previous barriers to adoption and application.

Controlling Superhydrophobicity on Complex Substrates Based on a Vapor-Phase Sublimation and Deposition Polymerization.

The superhydrophobic properties of material surfaces have attracted significant research and practical development in a wide range of applications. In the present study, a superhydrophobic coating was fabricated using a vapor-phase sublimation and deposition process. This process offers several advantages, including a controllable and tunable superhydrophobic property, a dry and solvent-free process that uses well-defined water/ice templates during fabrication, and a coating technology that is applicable to various substrates, regardless of their dimensions or complex geometric configurations. The fabrication process exploits time-dependent condensation to produce ice templates with a controlled surface morphology and roughness. The templates are sacrificed via vapor sublimation, which results in mass transfer of water vapor out of the system. A second vapor source of a polymer precursor is then introduced to the system, and deposition occurs upon polymerization on the iced templates, replicating the same topologies from the iced templates. The continuation of the co-current sublimation and deposition processes finally renders permanent hierarchical structures of the polymer coatings that combine the native hydrophobic property of the polymer and the structured property by the sacrificed ice templates, achieving a level of superhydrophobicity that is tunable from 90° to 164°. The experiments demonstrated the use of [2,2]paracyclophanes as the starting materials for forming the superhydrophobic coatings of poly(p-xylylenes) on substrate surfaces. In comparison to conventional vapor deposition of poly(p-xylylenes), which resulted in dense thin-film coatings with only a moderate water contact angle of approximately 90°, the reported superhydrophobic coatings and fabrication process can achieve a high water contact angle of 164°. Demonstrations furthermore revealed that the proposed coatings are durable while maintaining superhydrophobicity on various substrates, including an intraocular lens and a cardiovascular stent, even against harsh treatment conditions and varied solution compositions used on the substrates.

Heat Flux Analysis and Assessment of Drying Kinetics during Lyophilization of Fruits in a Pilot-Scale Freeze Dryer.

Vacuum freeze-drying as a process for achieving high product quality has attracted increasing attention in the last decade. Particularly in the pharmaceutical field and food processing industries, lyophilization can produce high-quality products compared to samples dried by conventional methods. Despite its benefits, lyophilization is a time-consuming and costly process that requires optimization of a number of process parameters, including shelf temperature, chamber pressure, freezing rate, and process time. This paper reports on the implementation of heat flux measurements that allow noninvasive real-time determination of the endpoint of the primary drying stage as an essential parameter for the effective optimization of the overall drying time. Quantitative analysis of the drying kinetics of five fruits (kiwifruit, avocado, Asian pear, persimmon, and passion fruit) was assessed by comparing the heat flux and temperature profiles of samples during the lyophilization process. For a 24 h lyophilization cycle, average heat fluxes in the primary drying phase ranged from 250 to 570 W/m2. A significant correlation was found between the temperature and heat flux distributions at the estimated endpoint of the sublimation process and the corresponding transition into the secondary drying stage. Furthermore, good agreement was also found for the freezing phase. The use of real-time heat flux measurements proved to be a cost-effective experimental method to better understand the process variables in order to reduce the lyophilization cycle time and overall energy consumption.

Comparison of Sublimation 3D Scanning Sprays in Terms of Their Effect on the Resulting 3D Scan, Thickness, and Sublimation Time.

This study compared eight sublimation scanning sprays in terms of their effect on 3D scanning results, coating thickness, and sublimation time. The work used an automated spraying system to ensure the same deposition conditions for all tested materials. All experiments were performed under the same environmental conditions to exclude the influence of the ambient environment on the coatings. All tested scanning sprays created coatings with thicknesses in the order of tens of micrometers that were detectable by the 3D scanner Atos III Triple Scan. The coatings must be applied carefully when accurate measurements are required. All used materials enabled the capture of the highly reflective surface of the Si-wafer. However, the differences between some sprays were significant. Sublimation time measurements showed that all coatings disappeared from the Si-wafer surface completely. Nevertheless, all coatings left visible traces on the mirror-like surface. They were easily wiped off with a cloth.

Experimental study on a novel vacuum sublimation-rehydration thawing of frozen potatoes.

To realize a quick thawing of frozen potatoes, the experimental investigation of thawing performance was conducted by using a novel vacuum sublimation-rehydration thawing (VSRT) in this study. Frozen diced potatoes (20 mm × 20 mm × 20 mm) with a total mass of 1.5 kg were selected as the thawing object. The center temperature of the frozen diced potato was raised from -18°C to 5°C to assess the beginning and end of thawing. The effects of sublimation time, heating plate temperature, and rehydration temperature on thawing time of frozen potatoes were experimentally studied. The VSRT and vacuum steam thawing (VST) were compared in terms of thawing time, hardness, and specific energy consumption. The results showed that the conditions of sublimation time of 25 min, heating plate temperature of 30°C, and rehydration temperature of 100°C could effectively shorten the thawing time of VSRT for thawing frozen potatoes. The thawing time of VSRT was only 49% of that of VST. Compared to the hardness of frozen potatoes thawed by VST, the hardness of frozen potatoes thawed by VSRT was closer to that of blanched (unfrozen) potatoes. The specific energy consumption of VSRT was lower than that of VST. PRACTICAL APPLICATION: The quality of frozen potatoes is directly affected by the thawing method used. A novel vacuum sublimation-rehydration thawing was conducted in this study, which can provide a new idea for a reasonable, effective, and quick thawing method for frozen potatoes.

A Non-Isothermal Pore Network Model of Primary Freeze Drying.

In this work, a non-isothermal pore network (PN) model with quasi-steady vapor transport and transient heat transfer is presented for the first time for the application of primary freeze drying. The pore-scale resolved model is physically based and allows for the investigation of correlations between spatially distributed structure and transport conditions. The studied examples were regular PN lattices with a significantly different structure, namely a spatially homogeneous PN, also denoted as monomodal PN, and a PN with significant structure variation, referred to as bimodal PN because of its bimodal pore size distribution. The material properties selected for the solid skeleton in this study are equivalent to those of maltodextrin. The temperature ranges applied here were -28 °C to -18 °C in the PN and -42 °C in the surrounding environment. The environmental vapor pressure was 10 Pa. The PNs were dried with constant temperature boundary conditions, and heat was transferred at the top side by the vapor leaving the PN. It is shown how the structural peculiarities affect the local heat and mass transfer conditions and result in a significant widening of the sublimation front in the case of the bimodal PN. The possibility of spatially and temporally resolved front structures is a unique feature of the PN model and allows the study of situations that are not yet described by classical continuum approaches, namely heterogeneous frozen porous materials. As demonstrated by the thin layers studied here, the pore-scale simulations are of particular interest for such situations, such as in lyomicroscopes or collagen scaffolds, where a length-scale separation between dry and ice-saturated regions is not possible.

Preparation of Mixed Few-Layer GeSe Nanosheets with High Efficiency by the Thermal Sublimation Method.

Two-dimensional (2D) GeSe has been proven promising in fast and broadband optoelectronic applications for its complicated band structure, inert surface property, and excellent stability. The major challenge is the deficiency of the effective technique for controllably prepared large-scale few-to-monolayer GeSe films. For this purpose, a layer-by-layer thinning method by thermal sublimation for manufacturing large-scale mixed few-layer GeSe with direct bandgaps is proposed, and an optimized sublimation temperature of 300 °C in vacuum is evaluated by atomic force microscopy. Scanning electron microscopy, transmission electron microscopy, energy-dispersive spectra, and fluorescence mapping measurements are performed on the thinned GeSe layers, and results are well-indexed to the orthorhombic lattice structure with direct bandgaps with an atomic ratio of Ge/Se ≈ 5:4. Raman and fluorescence spectra show an α-type crystalline structure of the thinned GeSe films, indicating the pure physical process of the sublimation thinning. Both the bulk and few-layer GeSe films demonstrate broadband absorption. Conductivity of the few-layer GeSe device indicates the overall crystalline integrity of the film after thermal thinning. Given the convenience and efficiency, we provide an effective approach for fabrication of large-scale 2D materials that are difficult to be prepared by traditional methods.

The effect of particle size on the sublimation behavior of butylhydroxytoluene as antioxidant in tablets during storage and coating.

The effect of particle size on the sublimation behavior of butylhydroxytoluene (BHT) was investigated when BHT was included as antioxidant in tablets. Sublimation of pure BHT was found to be independent of its particle size, with pore formation on the surface of all tablets after storage at room temperature and above. Moreover, a higher residual BHT content after storage was detected in tablets containing a larger size fraction. X-ray µCT scans revealed the formation of peripherally larger pores at higher BHT particle sizes, implying a slower sublimation rate in the tablet core. A stability study indicated an increase in the extent of BHT sublimation at higher temperature and longer exposure time for all size fractions. The influence of BHT particle size was more pronounced when the tablets were stored at higher temperature, but the effect receded with longer exposure time. Similar trends were seen in film-coated tablets. Due to the short exposure time to elevated temperatures, a gradient in pore size was also observed at smaller particle sizes, with peripheral pores being larger in uncoated tablets. Superficial pores disappeared when a film coating was deposited onto the tablets. After storage of the film-coated tablets, less BHT had sublimated compared to the uncoated tablet. The coating layer did not prevent sublimation, but the process was slowed down.

Empowerment: Freud, Canguilhem and Lacan on the ideal of health promotion.

Empowerment is a prominent ideal in health promotion. However, the exact meaning of this ideal is often not made explicit. In this paper, we outline an account of empowerment grounded in the human capacity to adapt and adjust to environmental and societal norms without being completely determined by those norms. Our account reveals a tension at the heart of empowerment between (a) the ability of self-governance and (b) the need to adapt and adjust to environmental and societal norms. We address this tension by drawing from the work of Freud, Canguilhem, and Lacan. First, we clarify through a discussion of Freud's notion of sublimation that it is difficult to assess empowerment independent of any social valuations, but also that it is no less problematic to make it dependent on social valuations alone. Second, we draw from the work of Canguilhem to show how empowerment can be understood in terms of the individual's capacity to tolerate the aggressions of a multiplicity of environments. Third, using Lacan, we show how empowerment requires incorporation of social and symbolic norms, without necessarily rendering ourselves a mere product of these norms. Finally, we demonstrate how the views of these authors can complement one another, resulting in a more sophisticated understanding of empowerment.

Theoretical Prediction of the Sublimation Behavior by Combining Ab Initio Calculations with Statistical Mechanics.

We develop a theoretical model to predict the sublimation vapor pressure of pure substances. Moreover, we present a simple monoatomic molecule approximation, which reduces the complexity of the vapor pressure expression for polyatomic gaseous molecules at a convincing level of accuracy, with deviations of the Arrhenius prefactor for NaCl and NaF being 5.02% and 7.08%, respectively. The physical model is based on ab initio calculations, statistical mechanics, and thermodynamics. We illustrate the approach for Ni, Cr, Cu (metallic bond), NaCl, NaF, ZrO2 (ionic bond) and SiO2 (covalent bond). The results are compared against thermodynamic databases, which show high accuracy of our theoretical predictions, and the deviations of the predicted sublimation enthalpy are typically below 10%, for Cu even only 0.1%. Furthermore, the partial pressures caused by gas phase reactions are also explored, showing good agreement with experimental results.

Arene-Perfluoroarene Force Driven Sublimation-Removable Chiral Coassemblies.

Multiple constituent coassembly is an emerging strategy to manipulate supramolecular chirality and chiroptical properties such as circularly polarized luminescence (CPL). However, the second or third constituent could not be removed from pristine self-assembly. Here we developed a constitute-removable chiral coassembly using sublimation that could realize coassembly with tunable supramolecular chirality, luminescence and CPL properties. Octafluoronapthalene (OFN) with small sublimation enthalpy formed coassemblies with perylene-conjugated peptoids via arene-perfluoroarene (AP) interaction that induced the emergence of macroscopic chirality and hypsochromic luminescence from yellow to green. Coassembly with OFN accelerated one-dimensional growth and induced the emergence of macroscopic chirality and CPL. Despite the stability at ambient conditions, vacuum-treatment triggered fast sublimation of OFN, which behaved as a sacrificial template. Physical removal of OFN retained the helical nanoarchitectures as well as the basic features of Cotton effects and CPL activities. X-ray diffraction suggested the back-fill consolidation occurred on the molecular voids by OFN removal that slightly varied the templated molecular arrangements. Sublimation of perfluorinated building units is green and efficient and non-destructive, which is potentially applicable in constructing template-directed chiroptical materials and devices.

CALPHAD-Based Modelling of the Temperature-Composition-Structure Relationship during Physical Vapor Deposition of Mg-Ca Thin Films.

The temperature-dependent composition and phase formation during the physical vapor deposition (PVD) of Mg-Ca thin films is modeled using a CALPHAD-based approach. Considering the Mg and Ca sublimation fluxes calculated based on the vapor pressure obtained by employing thermochemical equilibrium calculations, the experimentally observed synthesis-temperature trends in the thin-film composition and phase formation were reproduced. The model is a significant step towards understanding how synthesis parameters control composition and, therefore, phase formation in the PVD of metals with high vapor pressures.

ZIF-derived Co nanoparticles embedded into N-doped carbon nanotube composites for highly efficient electrochemical detection of nitrofurantoin in food.

Designing efficient and sensitive methods for the detection of nitrofurantoin (NFT) residues is of great importance for food safety and environmental protection. Herein, a composite with cobalt nanoparticles encapsulated in nitrogen-doped carbon nanotube (N/Co@CNTs@CC-II) was synthesized by in-situ growth and sublimation-gas phase transformation strategy and used to establish an ultrasensitive electrochemical sensor for NFT determination. The N/Co@CNTs@CC-II sensor exhibits uniform N doping, fine hollow structure, and abundant active metal sites, which lays a solid foundation for the ultra-sensitive detection of NFT. Benefiting from these advantages, the N/Co@CNTs@CC-II exhibits excellent sensitivity (8.19 µA µM-1 cm-2) and low detection limit (18.41 nM) for NFT detection. The practical feasibility of N/Co@CNTs@CC-II was also demonstrated by the determination of NFT in milk and tap water samples. This study may open up new opportunities for the application of N-doped carbon nanotube materials encapsulating transition metals.

Nanoporous GaN by selective area sublimation through an epitaxial nanomask: AlN versus SixNy.

Nanoporous GaN layers were fabricated using selective area sublimation through a self-organized AlN nanomask in a molecular beam epitaxy reactor. The obtained pore morphology, density and size were measured using plan-view and cross-section scanning electron microscopy experiments. It was found that the porosity of the GaN layers could be adjusted from 0.04 to 0.9 by changing the AlN nanomask thickness and sublimation conditions. The room temperature photoluminescence properties as a function of the porosity were analysed. In particular, a strong improvement (>100) of the room temperature photoluminescence intensity was observed for porous GaN layers with a porosity in the 0.4-0.65 range. The characteristics of these porous layers were compared to those obtained with a SixNynanomask. Furthermore, the regrowth of p-type GaN on light emitting diode structures made porous by using either an AlN or a SixNynanomask were compared.