Additional Short-range Force Research Articles

Ultraviolet Irradiation Suppresses Adhesion on TiO2

Environmental concerns have recently spurred a quest for materials that stay clean, such as TiO2, when subjected to the combined action of sunlight irradiation and exposure to rain. However, the fundamental mechanism that governs the self-cleaning properties of TiO2 still needs to be elucidated. TiO2 is known to be photocatalytic as well as to decompose organic adsorbents, but these properties do not explain its capacity to eliminate mineral contaminants. In the present paper, we report that hydrophilic UV-irradiated TiO2 layers are nonadhesive in the presence of water, thus preventing adhesion of mineral particles. Surface force measurements done using atomic force microscopy reveal the presence of an additional short-range repulsive force, which screens the van der Waals attractive forces, while long-range interactions are preserved. This additional short-range force does not originate from UV-induced trapping of surface charges or OH group creation, as we demonstrate by second harmonic generation and ambient pressure X-ray photoelectron spectroscopy investigations. This short-range repulsive force, which appears to be intrinsic to the TiO2 surface, is certainly a key phenomenon for a strong self-cleaning capacity.

Reply to ‘Comments on ‘Constraints on non-Newtonian gravity from the experiment on neutron quantum states in the Earth's gravitational field’’

Comment (Zimmer and Kaiser 2006 Class. Quantum Grav. 23 6077–80) contains three main statements: (1) a criticism of our method (Nesvizhevsky and Protasov 2004 Class. Quantum Grav. 21 4557–66; Nesvizhevsky and Protasov 2005 J. Res. Natl Inst. Stand. Technol.110 269–72) to calculate constraints on additional short-range forces using results obtained in (Nesvizhevsky et al 2002 Nature 415 297–9; Nesvizhevsky et al 2003 Phys. Rev. D 67 102002; Nesvizhevsky et al 2005 Eur. Phys. J.C 40 479–91), (2) a proposed method to improve these constraints using other low-energy neutron experiments and (3) a conclusion that other experiments could provide better constraints. We will show that the statements (1) and (2) are not correct and the statement (3) is not new.

Sum rules for the one-component plasma with additional short-range forces

It is proved that, in the one-component plasma, with interactions including a non-Coulombic short-range part, the density derivative of the correlation functions {rho}{sub n}(r{sub 1},...,r{sub n}) can be simply expressed as an integral of {rho}{sub n+1}(r{sub 1},...,r{sub n+1}). This result is applied to prove the relation between the fourth moment of {rho}{sub 2} and the compressibility.

An ion-exchange model for thylakoid stacking in chloroplasts

1. Introduction Chloroplasts of higher plants contain stacks of internal membranes (thylakoids). These stacks (grana) can be reversibly unstacked in vitro by changing the salt composition ln the chloroplast suspension [I]. Attempts have been made to explain the mechanism of stacking in terms of the classical theory of colloidal particle interactions which involve the interplay of electrostatic and van der Waals’ forces [2]. In a [3] a quantitative analysis of these forces led to the conclu- sion that an additional short range force [4] was required to explain stacking. It was also estimated that for the stacking to occur the net surface charge density on the grana membranes should be <l electronic charge (1 e)/3000 A’. Such a density is low when compared with the density expected from the full dissociation of surface acidic groups of proteins and lipids [3]. The required low net surface charge density in the stacked regions of the membranes can arise from one of two possible mechanisms [3]: (a) cation binding [S--8]; or (b) redistribution of charges between grana (stacked) and stroma (unstacked) portions of the thylakoid mem- brane [9-l 11. Here, we present a model involving binding of cations which explains the mechanism of stacking. The model is inspired by recent studies on the nature of short range repulsive forces between lipid bilayers [4,12,13] and mica surfaces [13-161. 2. Balance of forces For phospholipid or lecithin bilayers in water an additional repulsive force arises at distances below -30 A [4,12]. This so called ‘hydration’ force domi- nates the interactions between the bilayers at the short distances. The origin of this additional force between mica surfaces has been studied in detail