W odróżnieniu od obiektów makroskopowych, własności układów o rozmiarach nanometrycznych silnie zależą od ich wielkości i kształtu. Wynika to z faktu, iż większość atomów nanoobiektów znajduje się na ich powierzchni, i ich ich energia kohezji jest mniejsza niż atomów wewnątrz układu. Pokażemy, że gęstość gazu zamkniętego w objętości (w porze) o rozmiarach nanometrycznych, ograniczonej nieoddziaływującymi ścianami jest niejednorodna, i mniejsza (średnio) niż gęstość gazu w skali makroskopowej. Niejednorodność rozkładu gęstości maleje gdy rozmiary układu rosną, i jest zaniedbywalna dla obiektów o rozmiarach powyżej 5 nm. Z drugiej strony, gdy rozmiary poru maleją, gęstość gazu zbliża się do wartości gęstości gazu doskonałego. Efet ten należy odróżnić od niejednorodności gęstoci gazów zaadsorbowanych w nanoporach, spowodowanej różnicą siły oddziaływania gaz-gaz i gaz-adsorbent, która zmienia się wraz z odległością od adsorbenta. Wynik ten ma fundamentalne znaczenie w opisie ilościowym zjawisk adsorpcji, i poprawnym oszacowaniu adsorpcji całkowitej i nadmiarowej w nanoporach. Obie wielkości są obliczane zakładając stałą i jednorodną gęstość gazu w danych warunkach termodynamicznych (p,T), wyznaczoną dla obiektów makroskopowych. Ponadto objętość zajmowana przez gaz w nanoporach nie jest prosta i jednoznaczna do zdefiniowania. Tymczasem obie wielkości: objętość poru i gęstość gazu jaki można pomieścić (bez adsorbcji) w nanoporze są wielkościami niezbędnymi dla poprawnej ilościowej interpretacji eksperymentalnych izoterm adsorbcji. Przeanalizujemy ten aspekt na przykładzie sześciu gazów : badanych intensywnie nośników energii H2 i CH4, używanych do charakteryzacji materiałów porowatych N2, Ar i Kr, oraz CO2, podstawowego gazu cieplarnianego. Praca wykonana w ramach grantu French National Research Agency ANR, grant HYSTOR no. ANR-14-CE05-0009.

Maszyny molekularne [1], zwane także nano-maszynami, są obiektami w skali nanometrycznej, które mogą wykonywać ruchy translacyjne i/lub rotacyjne charakterystyczne dla urządzenie mechanicznych. Synteza tego typu nano-obiektów, to jest nowa rozwijająca się dziedzina, której znaczenie zostało potwierdzone przez przyznanie nagrody Nobla w dziedzinie chemii w 2016 roku [2-4]. W niniejszej prezentacji dyskutujemy rozwój tej dziedziny od czasów Richard’a Feynmann’a [5] do czasów współczesnych, z akcentem na aktualny ‘state of art’ w tej działalności.Przedstawimy koncepcję molekularnego motoru [6] i przedyskutujemy rożne aspekty związane z jego funkcjonowaniem: źródła energii, wpływ masy i lepkości otoczenia, oraz rolę ruchów Browna, a tym samym zwrócimy uwagę na termodynamiczne nierównowagowe aspektu nano-systemów.

At the nanoscale the positions of coexistence lines on the phase diagrams are shifted and their new locations depend mainly on the size and shape of the nano-confinement, the structure of the confining walls, and their interaction with the confined substance. Here we show that it is possible to induce structural transformations in a confined system by simply varying the number of molecules adsorbed in the pore. We found that the mechanism of these novel, adsorption-induced structural transformation in nano-pores differs from the capillary condensation. First, the structure of the confined gas is determined by a competition between adsorption sites attractive forces and intermolecular interaction. Second, at low temperature, the transformation is discontinuous because it is defined by limited number of adsorption sites [1,2]. The confined, equilibrium structures are not characterized by mean positions of molecules but rather by a probability distribution of molecular positions around adsorption centres. This distribution changes when the number of molecules in the pore increases. The character of transformation is temperature dependent: strongly discontinuous at low temperature, it evolves into a continuous transition when the temperature increases. The mechanism of the transformation is also modified when the size of the gas molecules and types of interaction change. In particular, we report the existence of the intermediate phase, observed only above a critical strength of the attractive interactions. This work was supported by the Polish National Science Centre (NCN, grant no. 2015/17/B/ST8/00099). The calculations have been partially performed at the WCSS computer center of The Wroclaw University of Science and Technology, grant no 33.

Unlike macroscopic objects, any system of nanometric size shows characteristics that strongly depend on its size and geometric form. It is the consequence of the fact that the major part of atoms (or molecules) of nano-object is located at its surface, and their cohesive energy is smaller than for the atoms in the bulk. Here we show that when a fluid is confined in nano-volume, delimited by non-interacting pore walls, its density is heterogeneous, decreases close to the pore wall, and, on average, is smaller than the density of bulk fluid. The heterogeneity of distribution of fluid density, resulting from the nano-confinement, progressively weakens when the pore size increases, and totally disappears for pores larger than 5 nm. On the other side, in the limit of very small pores, the fluid density approaches the ideal gas value. This effect should be distinguished from the well know heterogeneity of density of fluids adsorbed in nanopores, driven by the difference between the strength of fluid-fluid and fluid-pore wall interactions, that varies with the distance from the pore wall. The reported observation has non-trivial influence on evaluation of excess/total adsorption in nanopores, as these two quantities are calculated assuming the known – and homogeneous – bulk density of gas in the pore. Additionally, the gas density in the pores depends on the definition of the pore volume which is neither straightforward nor unique. The right estimation of both: pore volume and gas density is essential for quantitative interpretation of experimental adsorption isotherms: evaluation of pore size distribution and of the amount of adsorbed gas. We analyze this problem on an example of five gases: H2, CH4, the two intensively studied energy vectors, and N2, Ar, and Kr, commonly used for characterization of porous structures. For H2, the distributions of densities of gas confined in adsorbing and not adsorbing pores are compared and commented. This work was supported by the French National Research Agency ANR, grant HYSTOR no. ANR-14-CE05-0009.

Unlike macroscopic objects, any system of nanometric size shows characteristics that strongly depend on its size and geometric form. It is the consequence of the fact that the major part of atoms (or molecules) of nano-object is located at its surface, their cohesive energy is smaller than for the atoms in the bulk. Here we show that when a fluid is confined in nano-volume, delimited by non-interacting pore walls, its density is heterogeneous, decreases close to the pore wall, and, on average, is smaller than the density of bulk fluid. The heterogeneity of distribution of fluid density, resulting from the nano-confinement, progressively weakens when the pore size increases, and totally disappears for pores larger than 5 nm. On the other side, in the limit of very small pores, the fluid density approaches the ideal gas value. This effect should be distinguished from the well know heterogeneity of density of fluids adsorbed in nanopores, driven by the difference between the strength of fluid-fluid and fluid-pore wall interactions, that varies with the distance from the pore wall. The reported observation has non-trivial influence on evaluation of excess/total adsorption in nanopores, as these two quantities are calculated assuming the known – and homogeneous – bulk density of gas in the pore. Additionally, the gas density in the pores depends on the definition of the pore volume which is neither straightforward nor unique. The right estimation of both: pore volume and gas density is essential for quantitative interpretation of experimental adsorption isotherms: evaluation of pore size distribution and of the amount of adsorbed gas. We analyze this problem on an example of five gases: H2, CH4, the two intensively studied energy vectors, and N2, Ar, and Kr, commonly used for characterization of porous structures. For H2, the distributions of densities of gas confined in adsorbing and not adsorbing pores are compared and commented.

At the nanoscale the positions of coexistence lines on the phase diagrams are shifted and their new locations depend mainly on the size and shape of the nano-confinement, the structure of the confining walls, and their interaction with the confined substance. Here we show that it is possible to induce structural transformations in a confined system by simply varying the number of molecules adsorbed in the pore. We found that the mechanism of these novel, adsorption-induced structural transformation in nano-pores differs from the capillary condensation. First, the structure of the confined gas is determined by a competition between adsorption sites attractive forces and intermolecular interaction. Second, at low temperature, the transformation is discontinuous because it is defined by limited number of adsorption sites1,2.The confined, equilibrium structures are not characterized by mean positions of molecules but rather by a probability distribution of molecular positions around adsorption centres. This distribution transforms when the number of molecules in the pore increases. The character of transformation depends on temperature: it is strongly discontinuous at low temperature but evolves into a continuous transition when the temperature increases. Here we show how the mechanism of the transformation is modified by temperature and also by different types of interaction and the size of the gas molecules. In particular, the existence of the intermediate phase is observed only above a critical strength of the attractive interactions.

Phase changes are ubiquitous in nature, and transformations between solid structures represent a large group of them. They are usually reported on phase diagrams, as coexistence lines between different structures. The phase diagrams, well established for macroscopic 3-dimensional (3D) materials, change drastically when the material’s dimensions are reduced to few nanometers, or if the material is confined in a nano-pore. At the nanoscale the positions of coexistence lines on the phase diagrams are shifted and their new locations depend mainly on the size and shape of the nano-confinement, the structure of the confining walls, and their interaction with the confined substance. Here we show that it is possible to induce structural transformations in a confined system by simply varying the number of molecules adsorbed in the pore. We found that the mechanism of these novel, adsorption-induced structural transformation in nano-pores differs from that of well-known capillary condensation. The confined, equilibrium structures are not characterized by mean positions of molecules but rather by a probability distribution of molecular positions around adsorption centres. The character of transformation depends on temperature: it is strongly discontinuous at low temperature but evolves into a continuous transition when the temperature increases.