Aggregation effects on evaporation and the air/water interface of dodecyltrimethylammonium hydroxide solutions

 The system dodecyltrimethylammonium hydroxide (DTAOH)–water was studied by surface tension, ion-selective electrodes and evaporation in an electrobalance. Results confirmed earlier conclusions about a stepwise aggregation mechanism in DTAOH solutions. The aggregation process started at a total concentration C _T=(2.51±0.10)×10^-4 mol dm^-3) which probably corresponds to the formation of dimers. At C _T= (1.300±0.041)×10^-3 mol dm^-3 there was a change in the surface and evaporation behavior, corresponding to the formation of small, fully ionized aggregates which grew with increasing concentration. At C _T= (1.108±0.010)×10^-2 mol dm^-3 the formation of true micelles with hydroxide counterions in the Stern layer did not change significantly the evaporation and adsorption behavior. This means that between this concentration and C _T=(3.02±0.28)× M28.8n10^-2 mol dm^-3, the changes in structure were gradual. At the latter concentration there was a sudden change in the monolayer state at the air/water interface, with a strong surfactant desorption, and a major change in evaporation behavior. The changes are compatible with the formation of few, large aggregates reducing the total concentration of kinetically independent solute units, which in turn increased the activity of the solvent. This phenomenon is in agreement with literature information. The reduction in the evaporation rate of water was mainly due to the reduction of the water activity, caused by colligative effects. The reduction of the effective area available for evaporation had only a slight effect in water evaporation. Received: 9 January 1997 Accepted: 19 October 1997     

The thermodynamic properties of 2-ethylhexyl acrylate over the temperature range from <Emphasis Type="Italic">T</Emphasis> → 0 to 350 K

The temperature dependence of the heat capacity C _p ^o= f(T) 2 of 2-ethylhexyl acrylate was studied in an adiabatic vacuum calorimeter over the temperature range 6–350 K. Measurement errors were mainly of 0.2%. Glass formation and vitreous state parameters were determined. An isothermic shell calorimeter with a static bomb was used to measure the energy of combustion of 2-ethylhexyl acrylate. The experimental data were used to calculate the standard thermodynamic functions C _p ^o(T), H ^o(T)-H ^o(0), S ^o(T)-S ^o(0), and G ^o(T)-H ^o(0) of the compound in the vitreous and liquid states over the temperature range from T → 0 to 350 K, the standard enthalpies of combustion Δ_c H ^o, and the thermodynamic characteristics of formation Δ_f H ^o, Δ_f S ^o, and Δ_f G ^o at 298.15 K and p = 0.1 MPa.     

Heat capacity and heat content of BiNb<Subscript>5</Subscript>O<Subscript>14</Subscript>

The heat capacity and the heat content of bismuth niobate BiNb₅O₁₄ were measured by the relaxation time method, DSC and drop method, respectively. The temperature dependence of heat capacity in the form C _pm=455.84+0.06016T–7.7342·10⁶/T ² (J K^–1 mol^–1) was derived by the least squares method from the experimental data. Furthermore, the standard molar entropy at 298.15 K S _m=397.17 J K^–1 mol^–1 was derived from the low temperature heat capacity measurement.     

Studying Cu2–xSe phase transformation through DSC examination

The thermal effect accompanying the transition of Cu_2–xSe into a superionic conduction state was studied by non-isothermal measurements, at different heating and cooling rates (β=1, 2.5, 5, 10 and 20°C min^–1). During heating the peak temperature (T_p) remains almost stable for all values of β, (136.8±0.4°C for Cu₂Se and 133.0±0.3°C for Cu_1.99Se). A gradual shift of the initiation of the transformation towards lower temperatures is observed, as the heating rate increases. During cooling there is a significant shift in the position of the peak maximum (T_p) towards lower temperatures with the increase of the cooling rate. A small hysteresis is observed, which increases with the increase of the cooling rate, β. The mean value of transformation enthalpy was found to be 30.3±0.8 J g^–1 for Cu₂Se and 28.9±0.9 J g^–1 for Cu_1.99Se. The transformation can be described kinetically by the model f(ǯ)=(1–ǯ)^n(1+kcatX), with activation energy E=175 kJ mol^–1, exponent value n equal to 0.2, logA=20 and log(k_cat)= 0.5.     

Determination of thermodynamic stability of CdMoO4 by knudsen effusion vapor pressure measurement method

Thermodynamic stability of CdMoO₄ was determined by measuring the vapor pressures of Cd and MoO₃ bearing gaseous species. Th vaporization reaction could be described as CdMoO₄(s)+MoO₂(s) =Cd(g)+2/n(MoO₃)_n (n=3, 4 and 5). The vapor pressures of the cadmium (p _Cd) and trimer (p _(MoO3)3) measured in the temperature range 987≤T/K≤1111 could be expressed, respectively, as ln (p _Cd/Pa) = –32643.9/T+29.46±0.08 and ln(p _(MoO3)3/Pa) = –32289.6/T+29.28±0.08. The standard molar Gibbs free energy of formation of CdMoO₄(s), derived from the vaporization results could be expressed by the equations: °_f G _{CdMoO4 (s)} ⁰= –1002.0+0.267T±14.5 kJ mol^–1 (987≤T/K≤1033) and °_f G _{CdMoO4 (s)} ⁰ = –1101.9+0.363T±14.4 kJ mol^–1 (1044≤T/K≤1111). The standard enthalpy of formation of CdMoO₄(s) was found to be –1015.4±14.5 kJ mol^–1 .     

Thermal behaviour of transition-and tetravalentmetal oxides and phosphorous oxide composites

The heat capacity of the solid indium nitride was measured, using the Calvet TG-DSC 111 differential scanning microcalorimeter (Setaram, France), in the temperature between (314–978 K). The temperature dependence of the heat capacity can be presented in the following form: C _p=41.400+0.499·10⁻³ T−135502T ⁻²−26169900 T ⁻³.     

Heat capacity of crystalline GaN

The heat capacity of gallium nitride has been measured by DSC method using DuPont Thermal Analyst 2100, DSC 951 unit in the temperature range (300–850 K). The temperature dependence of the heat capacity can be presented in the following form: C _p=32.960+0.162·10⁻¹ T+2360170T ⁻²-775370000T ⁻³.     

Influence of molecular weight on the microhardness of poly(ethylene terephthalate)

 Poly(ethylene terephthalate) (PET) was annealed in vacuum at different temperatures (190–260 °C) for different times (10 min–24 h) in order to examine the mechanical properties (microhardness) of PET samples with a wide range of molecular weights (10 000–120 000). Short annealing times result in a twofold decrease in mol. wt. due to hydrolytic decomposition. However, long annealing times give rise to a substantial molecular weight increase. It is found that microhardness (H) rises linearly with the degree of crystallinity obtained during up-grading of mol. wt. and its extrapolation leads to H-values of completely crystalline PET, H ^PET _c=405 MPa for samples with conventional mol. wt. and of 426 MPa for samples with mol. wt. higher than 30 000. It is shown that the increase of mol. wt. for each set of samples with a given range of degree of crystallinity also causes a slight increase of H. The influence of mol. wt. upon hardness is discussed in the light of the changes in the physical structure (crystallinity, crystal thickness) which is formed at given heat treatment conditions. Received: 29 April 1997 Accepted: 23 September 1997     

Relationship Between Heat Capacity and Thermal Expansion Derived from the Lennard–Jones Potential

The relationship between heat capacity (C _p) and linear thermal expansion (α) derived from the Lennard–Jones potential is C _p=Aα(U ₀–E), where U ₀ is the heat of sublimation at T=0, E is the enthalpy and A is the coefficient. The values of A for different solidified inert gases coincide with one another within the limits of experimental error (±2%). The relationship is shown to be valid for various substances: solidified rare gases, diamond, halite and copper. This revised version was published online in July 2006 with corrections to the Cover Date.     

Determination of heat capacities of PbCrO4(s), Pb2CrO5(s), and Pb5CrO8(s)

Abstract  

Heat capacities of PbCrO₄(s), Pb₂CrO₅(s), and Pb₅CrO₈(s) were measured by differential scanning calorimetry. The measured heat capacities as a function of temperature are expressed as C _p <PbCrO₄> J K⁻¹ mol⁻¹ = 150.37 + 27.74 × 10⁻³ T − 2.80 × 10⁶ T ⁻² (T = 300–750 K), C _p <Pb₂CrO₅> J K⁻¹ mol⁻¹ = 194.55 + 76.09 × 10⁻³ T − 4.64 × 10⁶ T ⁻² (T = 300–700 K), and C _p  <Pb₅CrO₈> J K⁻¹ mol⁻¹ = 323.35 + 184.80 × 10⁻³ T − 5.48 × 10⁶ T ⁻² (T = 300–600 K). From the measured heat capacity data, thermodynamic functions such as enthalpy increments, entropies, and Gibbs energy functions were derived.     

Thermodynamic characteristics of triphenylantimony bis(acetophenoneoximate)

The temperature dependence of heat capacity C _p ^° = f(T) of triphenylantimony bis(acetophenoneoximate) Ph₃Sb(ONCPhMe)₂ was measured for the first time in an adiabatic vacuum calorimeter in the range of 6.5–370 K and a differential scanning calorimeter in the range of 350–463 K. The temperature, enthalpy, and entropy of fusion were determined. Treatment of low-temperature (20 K ≤ T ≤ 50 K) heat capacity was performed on the basis of Debye’s theory of the heat capacity of solids and its multifractal model and, as a consequence, a conclusion was drawn on the type of structure topology. Standard thermodynamic functions C _p ^°(T), H°(T) — H°(0), S°(T), and G°(T) — H°(0) were calculated according to the experimental data obtained for the compound mentioned in the crystalline and liquid states for the range of T → 0–460 K. The standard entropy of the formation of crystalline Ph₃Sb(ONCPhMe)₂ was determined at T = 298.15 K.     

Capacitance spectroscopy of alumina sol–gel capacitors with Al top contacts

We measured the complex capacitance C(f) of ITO/sol–gel alumina/Al capacitors deposited on glass (and some on stainless steel foil) in the frequency range 15 Hz–10 MHz. The sol–gel films were deposited by dip-coating and following a two-step process. The capacitance C(f) found was much higher than that of a pure Al₂O₃-film due to the remaining porosity of the film and the uptake of H₂O from the environment. The C(f) curves are useful as a sensitive probe for the porosity of the sol–gel film. In particular the evolution of the capacitance curve with time after drying has been measured. The curves can qualitatively be understood by modelling the capacitor as a (nearly) percolating random insulator/conductor network, using the effective medium approximation. However a detailed understanding of the relation between the C(f,t) curves and the structure of the films requires a more elaborate model. Films sintered at 500–550 °C for 1 h initially behave exactly as not sintered films but in contrast with the latter they improve slowly over time. Fast sintering yields better films.     

Heat capacity of methacetin in a temperature range of 6 to 300 K

Heat capacity of methacetin (N-(4-methoxyphenyl)-acetamide) has been measured in the temperature range 5.8–300 K. No anomalies in the C _p(T) dependence were observed. Thermodynamic functions were calculated. At 298.15 K, the values of entropy and enthalpy are equal to 243.1 J K⁻¹ mol⁻¹ and 36360 J mol⁻¹, respectively. The heat capacity of methacetin in the temperature range 6–10 K is well fitted by Debye equation C _p = AT ³. The thermodynamic data obtained for methacetin are compared with those for the monoclinic and orthorhombic polymorphs of paracetamol.     

The interface air/water of n-dodecanephosphonic acid solutions

 The air/water interface of the system n-dodecanephosphonic acid (H₂DP)–water was studied by surface tension, ion-selective electrodes and evaporation in an electrobalance. The combination of surface tension and ion-selective electrodes measurements enables to study the adsorption of soluble surfactants above the cmc using the Gibbs’ equation. H₂DP formed a nonideal monolayer at the air/water interface with A _molec=0.995 nm² below the cmc. Above the cmc there was a reduction in adsorption giving A _molec=6.32 nm², which remained almost constant in the explored concentration range. This adsorption reduction may be due to a change composition on micellization, or to a thermodynamic advantage of micellization on adsorption. The reduction in the evaporation rate of water was mainly due to the reduction of the water activity, caused by the presence of solutes in bulk. This is because the strong changes in the surface coverage did not have significant influence on the evaporation rate. Received: 6 January 1997 Accepted: 15 August 1997     

Standard molar enthalpies of formation and sublimation of <Emphasis Type="Italic">N</Emphasis>-phenylphthalimide

The standard (p ⁰=0.1 MPa) molar enthalpy of formation, Δ_f H ⁰ _m, for crystalline N-phenylphthalimide was derived from its standard molar enthalpy of combustion, in oxygen, at the temperature 298.15 K, measured by static bomb-combustion calorimetry, as –206.0±3.4 kJ mol^–1. The standard molar enthalpy of sublimation, Δ^g _cr H ⁰ _m , at T=298.15 K, was derived, from high temperature Calvet microcalorimetry, as 121.3±1.0 kJ mol^–1. The derived standard molar enthalpy of formation, in the gaseous state, is analysed in terms of enthalpic increments and interpreted in terms of molecular structure.     

Low-temperature thermodynamic properties of <Emphasis Type="Italic">L</Emphasis>-cysteine

Heat capacity C _p(T) of the orthorhombic polymorph of L-cysteine was measured in the temperature range 6–300 K by adiabatic calorimetry; thermodynamic functions were calculated based on these measurements. At 298.15 K the values of heat capacity, C _p; entropy, S _m⁰(T)-S _m⁰(0); difference in the enthalpy, H _m⁰(T)-H _m⁰(0), are equal, respectively, to 144.6±0.3 J K⁻¹ mol⁻¹, 169.0±0.4 J K⁻¹ mol⁻¹ and 24960±50 J mol⁻¹. An anomaly of heat capacity near 70 K was registered as a small, 3–5% height, diffuse ‘jump’ accompanied by the substantial increase in the thermal relaxation time. The shape of the anomaly is sensitive to thermal pre-history of the sample.     

Chain diffusion in the melt of an asymmetric diblock copolymer in the disordered and ordered state

 The self-diffusion in a polystyrene-b-polyisoprene diblock copolymer with a strongly asymmetric composition was investigated with dependence on temperature by pulsed field gradient (PFG) NMR. The diblock shows with decreasing temperature a disorder-to-order-transition at T _ODT=393 K from a micellar liquid-like to a bcc ordered state which was recently measured by SAXS [M. Schwab and B. Stühn, Phys. Rev. Lett. (1996) 76: 924]. Two diffusivities were observed, one of the free diblock chains and one of the diblock chains fixed in micelles. The volume fraction of free chains decreases with decreasing temperature. The diffusivity of the free chains must be related to chain stretching. The experiments show that within the time of the NMR experiment (300 ms) there is no exchange between the diblock chains in the free state and those fixed in the core of the micelles. Received: 25 March 1997 Accepted: 25 April 1997     

Non-debye nature in thermal relaxation and thermal properties of lithium borate glasses studied by modulated DSC

Complex heat capacity, C _p ^*=C _p ^'–iC _p ^', of lithium borate glasses xLi₂O·(1–x)B₂O₃ (molar fraction x=0.00–0.30) has been investigated by Modulated DSC. We have analyzed the shape of C _p ^* by the Cole-Cole plot, performed fitting by the Havriliak-Negami equation, and then determined the parameters related to the non-Debye nature of thermal relaxation. Moreover, the concentration dependence of the thermal properties has been investigated. Glass transition temperatures become higher with the increase of molar fraction of Li₂O and shows the board peak around x=0.26. Temperature ranges of glass transitions become narrower with the increase of Li₂O concentration.     

Thermodynamic Properties of Hydrofullerene C60H36 from 5 to 340 K

The temperature dependence of the molar heat capacity (C⁰ _p) of hydrofullerene C₆₀H₃₆ between 5 and 340 K was determined by adiabatic vacuum calorimetry with an error of about 0.2%. The experimental data were used for the calculation of the thermodynamic functions of the compound in the range 0 to340 K. It was found that at T=298.15 K and p=101.325 kPa C⁰ _p (298.15)=690.0 J K⁻¹ mol⁻¹,H^o(298.15)−H^o(0)= 84.94 kJ mol⁻¹,S^o(298.15)=506.8 J K⁻¹ mol⁻¹, G^o(298.15)−H^o(0)= −66.17 kJ mol⁻¹. The standard entropy of formation of hydrofullerene C₆₀H₃₆ and the entropy of reaction of its formation by hydrogenation of fullerene C₆₀ with hydrogen were estimated and at T=298.15 K they were Δ_fS^o= −2188.4 J K⁻¹ mol⁻¹ and Δ_rS^o= −2270.5 J K⁻¹mol⁻¹, respectively. This revised version was published online in July 2006 with corrections to the Cover Date.     

The thermodynamic functions of fullerene derivative (<Emphasis Type="Italic">t</Emphasis>-Bu)<Subscript>12</Subscript>C<Subscript>60</Subscript> over the temperature range from <Emphasis Type="Italic">T</Emphasis> → 0 to 420 K

The temperature dependence of heat capacity C _p ^o = f(T) of fullerene derivative (t-Bu)₁₂C₆₀ has been measured by a adiabatic vacuum calorimeter over the temperature range T = 6–350 K and by a differential scanning calorimeter over the temperature range T = 330–420 K for the first time. The low-temperature (T ≤ 50 K) dependence of the heat capacity was analyzed based on Debye’s the heat capacity theory of solids and its fractal variant. As a consequence, the conclusion about structure heterodynamicity is given. The experimental results have been used to calculate the standard thermodynamic functions C _p ^o (T), H ^o(T)−H ^o(0), S ^o(T) and G ^o(T) − H ^o(0) over the range from T → 0 to 420 K. The standard entropy of formation at 298.15 K of fullerene derivative under study was calculated. The temperature of decomposition onset of derivative was determined by differential scanning calorimetery and thermogravimetric analysis. The standard thermodynamic characteristics of (t-Bu)₁₂C₆₀ and C₆₀ fullerite were compared.