(Press-News.org) Although the van der Waals force was discovered around 150 years ago, it is still difficult to quantify when predicting the behaviour of solids, liquids, and molecules. Precise measurements were only possible up to now for single atoms or macroscopic objects. However, the van der Waals forces are particularly important at intermediate size, where they crucially co-determine the behaviour of complex molecules, such as biomolecules and proteins. They are also responsible for the functioning of certain adhesives and are the reason why geckos can adhere so amazingly well to surfaces, even allowing them to climb smooth walls.
"Using our method, we determined the van der Waals force for the first time for single molecules throughout a larger distance range," says Dr. Christian Wagner. The measured values agree with theoretical predictions, according to which the binding strength decreases with the cube of the distance - which explains the extremely small range of the interaction. It was also revealed that the bigger the molecule, the stronger its attraction to the surface. In reality, this effect is even stronger than simple models predict and also than would be intuitively assumed. "Usually, only the interaction of all those atoms involved is added together. But the van der Waals forces that we measured are 10 % higher than this," says the physicist from Jülich's Peter Grünberg Institute.
More room to manoeuvre leads to stronger bonds
What is the reason for the superlinear increase? The van der Waals force, to put it simply, emerges due to the displacement of electrons in the shells of atoms and molecules, caused by quantum fluctuations, which leads to a weak electrical attraction. In the case of larger molecules, more atoms are involved as each of these molecules also comprises more atoms. And on top of this, each and every atom contributes more strongly.
"As large organic molecules often form electron clouds that stretch across the entire molecule, they offer electrons considerably more room to manoeuvre than a single atom," says the head of the young investigators group at Jülich, Dr. Ruslan Temirov. "This makes them easier to displace, which overproportionally increases the electrical attraction."
Measuring the force with a tuning fork
For the measurements, the scientists affixed complex organic carbon compounds, which they had attached to a metal surface, to the tip of an atomic force microscope. They had secured this tip in turn to a vibration sensor so that the tip moved back and forth rapidly, a bit like a tiny tuning fork. When the molecules are removed from the surface, this vibrational frequency alters, allowing conclusions to be drawn in relation to the van der Waals forces, even when the tip is withdrawn a few molecule lengths (approx. 4 nanometres) from the surface.
The values determined are particularly interesting for simulation calculations using density functional theory, the development of which was honoured with the Nobel Prize in 1998. The technique is the most commonly used method today for calculating the structural, electronic, and optical properties of molecules and solids. Despite its many advantages, it still has problems correctly predicting the van der Waals forces.
INFORMATION:
Original publication:
Non-additivity of molecule-surface van der Waals potentials from force measurements
C. Wagner, N. Fournier, V. G. Ruiz, C. Li, K. Müllen, M. Rohlfing, A. Tkatchenko, R. Temirov, and F. S. Tautz
Nat. Commun. (published online 26 November 2014), DOI: 10.1038/ncomm6568
Further information:
Research at the Peter Grünberg Institute - Functional Nanostructures at Surfaces (PGI-3): http://www.fz-juelich.de/pgi/pgi-3/EN/Home/home_node.html
Young investigators group "Complex Transport Regimes in Low-Temperature Scanning Tunnelling Microscopy" headed by Dr. Ruslan Temirov at PGI-3: http://www.fz-juelich.de/pgi/pgi-3/EN/UeberUns/Organisation/Gruppe3/gruppe3_node.html
Contact:
Dr. Christian Wagner
Peter Grünberg Institute - Functional Nanostructures at Surfaces (PGI-3)
Tel. +49 2461 61-3538
c.wagner@fz-juelich.de
Press contact:
Tobias Schlößer
Corporate Communications (UK)
Tel: +49 2461 61-4771
t.schloesser@fz-juelich.de
This news release is available in French. The way people with autism spectrum disorder (ASD) gather information - not the judgement process itself - might explain why they gain different perceptions from peoples' faces, according to a new study from Hôpital Rivière-des-Prairies and the University of Montreal. "The evaluation of an individual's face is a rapid process that influences our future relationship with the individual," said Baudouin Forgeot d'Arc, lead author of the study. "By studying these judgments, we wanted to better understand how people with ...
The precise movements of a young hammerhead shark have been tracked for the first time and are published in the open access journal Animal Biotelemetry. The study, which ran over a 10-month period, reveals important gaps in current efforts to protect these endangered sharks and suggests key locations that should be protected to help the survival of the species.
Hammerhead sharks, which have recently received new protections from the UN Convention on the Conservation of Migratory Species of Wild Animals, are experiencing drastic population declines in excess of 90% in ...
The expression of a gene involved in female birds' color vision is linked to the evolution of colorful plumage in males, reports a new study from the University of Chicago. The findings, published Nov. 26 in the Proceedings of the Royal Society B, confirm the essential role of female color perception in mate selection and sexual dimorphism.
"This is the first time an aspect of the visual system in birds has been directly associated with plumage evolution," said Natasha Bloch, PhD, who authored the study while a graduate student in ecology & evolution at the University ...
Deaf teenagers have better reading skills if they were identified as deaf by the time they were nine months old, research from the University of Southampton has shown.
The Southampton team has been studying the development of a group of children who were identified with permanent childhood hearing impairment (PCHI) at a very early age in a pilot screening programme conducted in Southampton and London in the 1990s.
Follow up assessments when the children were aged eight showed those who were screened at birth had better language skills than those children who were not ...
Rheumatic heart disease (RHD) - the most common acquired heart disease in children in many countries of the world - is being neglected and poorly treated, according to new findings from the Global Rheumatic Heart Disease Registry (the REMEDY study), published online today (Wednesday) in the European Heart Journal [1].
RHD accounts for up to 1.4 million deaths every year, with the highest numbers of people affected by it and dying occurring in low and middle-income countries. It is triggered by rheumatic fever (RF) that can be prevented and controlled. RF is preceded by ...
The potential to quickly diagnose children with type 1 diabetes before the onset of serious illness could be achieved using a simple, non-invasive breath test, according to new research published today.
In one of the most comprehensive breath-based studies of children with type 1 diabetes performed to date, a team of researchers from Oxford, UK have linked a sweet-smelling chemical marker in the breath with a build-up of potentially harmful chemicals in the blood that accumulate when insulin levels are low.
It is hoped these results--linking an increased level of breath ...
University of Adelaide-led research will help pinpoint the impact of waves on sea ice, which is vulnerable to climate change, particularly in the Arctic where it is rapidly retreating.
Published today in the Proceedings of the Royal Society A, the research reports the first laboratory experiments testing theoretical models of wave activity in frozen oceans.
"Sea ice is both an indicator and agent of climate change," says project leader Dr Luke Bennetts, Research Fellow in the School of Mathematical Sciences.
"Sea ice covering the ocean surface is white and efficiently ...
Researchers have found that the spread of an exotic honey bee parasite -now found worldwide - is linked not only to its superior competitive ability, but also to climate, according to a new study published in the journal Proceedings of the Royal Society B.
The team of researchers, including Myrsini Natsopoulou from the Martin-Luther-Universität Halle-Wittenberg, who co-led the research alongside Dr. Dino McMahon from Queen's University Belfast, believes that the parasite could become more prevalent in the UK in the future and their findings demonstrate the importance ...
Taking folic acid before conception significantly reduces the risk of small for gestational age (SGA) at birth, suggests a new study published today (26 November) in BJOG: An International Journal of Obstetrics and Gynaecology (BJOG).
This UK population-based study and systematic review assessed the effect of timing of folic acid supplementation during pregnancy on the risk of the baby being SGA at birth, defined as birth weight less than the 10th centile or in the lowest 10% of babies born.
Being small for gestational age is associated with increased neonatal morbidity ...
The Institute of Medicine defines health literacy as the degree to which a person is able to obtain, understand, and process basic health information and services, so that s/he can make appropriate decisions about his/her health.
Low levels of health literacy among older adults are associated with poorer self-care, particularly of long term conditions, higher than average use of emergency care services, low levels of preventive care, and an overall increased risk of death.
The most important factor governing a decline in health literacy in later years is thought to ...
